feat: configurable rate limiting and comprehensive E2E test suite

Rate Limiting Configuration:
- Add ACKIFY_AUTH_MAGICLINK_RATE_LIMIT_EMAIL (default: 3/hour)
- Add ACKIFY_AUTH_MAGICLINK_RATE_LIMIT_IP (default: 10/hour)
- Add ACKIFY_AUTH_RATE_LIMIT (default: 5/min)
- Add ACKIFY_DOCUMENT_RATE_LIMIT (default: 10/min)
- Add ACKIFY_GENERAL_RATE_LIMIT (default: 100/min)

E2E Test Suite:
- 01-signature-workflow: Complete signature flow validation
- 02-signature-uniqueness: Constraint enforcement and duplicate prevention
- 03-admin-signers-management: Expected signers CRUD operations
- 04-admin-email-reminders: SMTP reminder functionality
- 05-document-creation-by-url: URL-based document initialization
- 06-my-signatures-page: User signature list and navigation
- 07-admin-document-deletion: Cascade deletion verification
- 08-admin-route-protection: Access control validation
- 09-complete-workflow: End-to-end multi-user scenario
- 10-unexpected-signatures: Handling of non-expected signers

backend/pkg/web/server.go

@@ -115,10 +115,12 @@ func NewServer(ctx context.Context, cfg *config.Config, frontend embed.FS, versi
 	}
 
 	magicLinkService := services.NewMagicLinkService(services.MagicLinkServiceConfig{
-		Repository:  magicLinkRepo,
-		EmailSender: emailSender,
-		BaseURL:     cfg.App.BaseURL,
-		AppName:     cfg.App.Organisation,
+		Repository:        magicLinkRepo,
+		EmailSender:       emailSender,
+		BaseURL:           cfg.App.BaseURL,
+		AppName:           cfg.App.Organisation,
+		RateLimitPerEmail: cfg.Auth.MagicLinkRateLimitEmail,
+		RateLimitPerIP:    cfg.Auth.MagicLinkRateLimitIP,
 	})
 
 	// Initialize Magic Link cleanup worker
@@ -178,6 +180,9 @@ func NewServer(ctx context.Context, cfg *config.Config, frontend embed.FS, versi
 		OAuthEnabled:              cfg.Auth.OAuthEnabled,
 		MagicLinkEnabled:          cfg.Auth.MagicLinkEnabled,
 		OnlyAdminCanCreate:        cfg.App.OnlyAdminCanCreate,
+		AuthRateLimit:             cfg.App.AuthRateLimit,
+		DocumentRateLimit:         cfg.App.DocumentRateLimit,
+		GeneralRateLimit:          cfg.App.GeneralRateLimit,
 	}
 	apiRouter := api.NewRouter(apiConfig)
 	router.Mount("/api/v1", apiRouter)