groupware: add /bootstrap

* add a GET /accounts/{a}/boostrap URI that delivers the same as GET /
   but also mailboxes for a given account, in case the UI remembers the
   last used account identifier, to avoid an additional roundtrip

 * streamline the use of simpleError()

 * add logging of errors at the calling site

 * add logging of evictions of Sessions from the cache

 * change default Session cache TTL to 5min instead of 30sec

pkg/structs/structs.go

@@ -2,6 +2,9 @@
 package structs
 
 import (
+	"maps"
+	"slices"
+
 	orderedmap "github.com/wk8/go-ordered-map"
 )
 
@@ -30,3 +33,11 @@ func Uniq[T comparable](source []T) []T {
 	}
 	return set
 }
+
+func Keys[K comparable, V any](source map[K]V) []K {
+	if source == nil {
+		var zero []K
+		return zero
+	}
+	return slices.Collect(maps.Keys(source))
+}

pkg/structs/structs_test.go

@@ -83,3 +83,19 @@ func TestUniqWithStructs(t *testing.T) {
 		})
 	}
 }
+
+func TestKeys(t *testing.T) {
+	tests := []struct {
+		input    map[int]string
+		expected []int
+	}{
+		{map[int]string{5: "cinq", 1: "un", 3: "trois", 4: "vier"}, []int{5, 1, 3, 4}},
+		{map[int]string{1: "un"}, []int{1}},
+	}
+	for i, tt := range tests {
+		t.Run(fmt.Sprintf("%d: testing %v", i+1, tt.input), func(t *testing.T) {
+			result := Keys(tt.input)
+			assert.ElementsMatch(t, tt.expected, result)
+		})
+	}
+}