fix: add missing service README.md files with basic description

services/app-provider/README.md

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+# App Provider
+
+The `app-provider` service provides the CS3 App Provider API for OpenCloud. It is responsible for managing and serving applications that can open files based on their MIME types.
+
+The service works in conjunction with the `app-registry` service, which maintains the registry of available applications and their supported MIME types. When a client requests to open a file with a specific application, the `app-provider` service handles the request and coordinates with the application to provide the appropriate interface.
+
+## Integration
+
+The `app-provider` service integrates with:
+- `app-registry` - For discovering which applications are available for specific MIME types
+- `frontend` - The frontend service forwards app provider requests (default endpoint `/app`) to this service
+- `gateway` - Routes requests to the app provider service
+
+## Configuration
+
+The service can be configured via environment variables. Key configuration options include:
+- `APP_PROVIDER_EXTERNAL_ADDR` - External address where the gateway service can reach the app provider
+
+## Scalability
+
+The app-provider service can be scaled horizontally as it primarily acts as a coordinator between applications and the OpenCloud storage layer.

services/groups/README.md

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+# Groups
+
+The `groups` service provides the CS3 Groups API for OpenCloud. It is responsible for managing group information and memberships within the OpenCloud instance.
+
+This service implements the CS3 identity group provider interface, allowing other services to query and manage groups. It works as a backend provider for the `graph` service when using the CS3 backend mode.
+
+## Backend Integration
+
+The groups service can work with different storage backends:
+- LDAP integration through the graph service
+- Direct CS3 API implementation
+
+When using the `graph` service with the CS3 backend (`GRAPH_IDENTITY_BACKEND=cs3`), the graph service queries group information through this service.
+
+## API
+
+The service provides CS3 gRPC APIs for:
+- Listing groups
+- Getting group information
+- Finding groups by name or ID
+- Managing group memberships
+
+## Usage
+
+The groups service is primarily used internally by other OpenCloud services rather than being accessed directly by clients. The `frontend` and `ocs` services translate HTTP API requests into CS3 API calls to this service.
+
+## Scalability
+
+Since the groups service queries backend systems (like LDAP through the configured identity backend), it can be scaled horizontally without additional configuration when using stateless backends.

services/sharing/README.md

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+# Sharing
+
+The `sharing` service provides the CS3 Sharing API for OpenCloud. It manages user shares and public link shares, implementing the core sharing functionality.
+
+## Overview
+
+The sharing service handles:
+- User-to-user shares (share a file or folder with another user)
+- Public link shares (share via a public URL)
+- Share permissions and roles
+- Share lifecycle management (create, update, delete)
+
+This service works in conjunction with the storage providers (`storage-shares` and `storage-publiclink`) to persist and manage share information.
+
+## Integration
+
+The sharing service integrates with:
+- `frontend` and `ocs` - Provide HTTP APIs that translate to CS3 sharing calls
+- `storage-shares` - Stores and manages received shares
+- `storage-publiclink` - Manages public link shares
+- `gateway` - Routes sharing requests
+- `graph` - Provides LibreGraph API for sharing with roles
+
+## Share Types
+
+The service supports different types of shares:
+- **User shares** - Share resources with specific users
+- **Group shares** - Share resources with groups
+- **Public link shares** - Create public URLs for sharing
+- **Federated shares** - Share with users on other OpenCloud instances (via `ocm` service)
+
+## Configuration
+
+Share behavior can be configured via environment variables:
+- Password enforcement for public shares
+- Auto-acceptance of shares
+- Share permissions and restrictions
+
+See the `frontend` service README for more details on share-related configuration options.
+
+## Scalability
+
+The sharing service depends on the configured storage backends for share metadata. Scalability characteristics depend on the chosen storage backend configuration.

services/storage-publiclink/README.md

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+# Storage PublicLink
+
+The `storage-publiclink` service provides storage backend functionality for public link shares in OpenCloud. It implements the CS3 storage provider interface specifically for managing public link shared resources.
+
+## Overview
+
+This service is part of the storage services family and is responsible for:
+- Storing metadata about public link shares
+- Providing access to publicly shared resources
+- Managing public link tokens and permissions
+- Handling anonymous access to shared content
+
+## Integration
+
+The storage-publiclink service integrates with:
+- `sharing` service - Creates and manages public link shares
+- `gateway` service - Routes requests to publicly shared resources
+- `frontend` and `ocdav` - Provide HTTP/WebDAV access to public links
+- Storage drivers - Accesses the actual file content
+
+## Storage Registry
+
+The service is registered in the gateway's storage registry with:
+- Provider ID: `7993447f-687f-490d-875c-ac95e89a62a4`
+- Mount point: `/public`
+- Space types: `grant` and `mountpoint`
+
+See the `gateway` README for more details on storage registry configuration.
+
+## Access Control
+
+Public link shares can be configured with:
+- Password protection
+- Expiration dates
+- Read-only or read-write permissions
+- Download limits
+
+## Scalability
+
+The storage-publiclink service can be scaled horizontally. When running multiple instances, ensure that the storage backend configuration is identical across all instances.

services/storage-shares/README.md

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+# Storage Shares
+
+The `storage-shares` service provides storage backend functionality for user and group shares in OpenCloud. It implements the CS3 storage provider interface specifically for managing shared resources.
+
+## Overview
+
+This service is part of the storage services family and is responsible for:
+- Storing metadata about user and group shares
+- Providing a virtual view of received shares
+- Managing share mountpoints
+- Handling access to resources shared by other users
+
+## Integration
+
+The storage-shares service integrates with:
+- `sharing` service - Creates and manages shares
+- `gateway` service - Routes requests to shared resources
+- `storage-users` service - Accesses the underlying file content
+- `frontend` and `ocdav` - Provide HTTP/WebDAV access to shares
+
+## Virtual Shares Folder
+
+The service provides a virtual "Shares" folder for each user where all received shares are mounted. This allows users to access all files and folders that have been shared with them in a centralized location.
+
+## Storage Registry
+
+The service is registered in the gateway's storage registry with:
+- Provider ID: `a0ca6a90-a365-4782-871e-d44447bbc668`
+- Mount point: `/users/{{.CurrentUser.Id.OpaqueId}}/Shares`
+- Space types: `virtual`, `grant`, and `mountpoint`
+
+See the `gateway` README for more details on storage registry configuration.
+
+## Scalability
+
+The storage-shares service can be scaled horizontally. When running multiple instances, ensure that the share metadata storage configuration is identical across all instances.

services/users/README.md

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+# Users
+
+The `users` service provides the CS3 Users API for OpenCloud. It is responsible for managing user information and authentication within the OpenCloud instance.
+
+This service implements the CS3 identity user provider interface, allowing other services to query and manage user accounts. It works as a backend provider for the `graph` service when using the CS3 backend mode.
+
+## Backend Integration
+
+The users service can work with different storage backends:
+- LDAP integration through the graph service
+- Direct CS3 API implementation
+
+When using the `graph` service with the CS3 backend (`GRAPH_IDENTITY_BACKEND=cs3`), the graph service queries user information through this service.
+
+## API
+
+The service provides CS3 gRPC APIs for:
+- Listing users
+- Getting user information
+- Finding users by username, email, or ID
+- User authentication and validation
+
+## Usage
+
+The users service is primarily used internally by other OpenCloud services rather than being accessed directly by clients. The `frontend`, `ocs`, and `graph` services translate HTTP API requests into CS3 API calls to this service.
+
+## Scalability
+
+Since the users service queries backend systems (like LDAP through the configured identity backend), it can be scaled horizontally without additional configuration when using stateless backends.