feat: task trash, triage trash and retention settings for every area; admin can forbid keeping things for good

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/domain/models.go

@@ -145,6 +145,10 @@ type User struct {
 	DoneRetentionDays int `json:"doneRetentionDays"`
 	// VoiceInput: "" uses the server's Whisper (when set up), "browser" the browser's recognition
 	VoiceInput string `json:"voiceInput"`
+	// Retention: how long finished and deleted things are kept (storage/retention.go);
+	// RetentionNeverAllowed: whether "nie" may be chosen on this server
+	Retention             *Retention `json:"retention,omitempty"`
+	RetentionNeverAllowed bool       `json:"retentionNeverAllowed"`
 }
 
 // NotificationSettings: which events reach a user over which channel, the daily summary and a pause.
@@ -410,6 +414,10 @@ type SystemSettings struct {
 	BackupEnabled       bool   `json:"backupEnabled"`
 	BackupTime          string `json:"backupTime"`
 	BackupRetentionDays int    `json:"backupRetentionDays"`
+	// RetentionAllowNever: people may keep finished and deleted things for good ("nie"); nil in an
+	// update leaves it unchanged. RetentionNeverViaEnv: fixed by RETENTION_ALLOW_NEVER, not editable.
+	RetentionAllowNever  *bool `json:"retentionAllowNever,omitempty"`
+	RetentionNeverViaEnv bool  `json:"retentionNeverViaEnv,omitempty"`
 }
 
 // UnmarshalJSON accepts smtpPort as text or number: older clients sent a number, which made the whole
@@ -682,3 +690,13 @@ type FolderShare struct {
 	CreatedBy  string `json:"createdBy"`
 	CreatedAt  string `json:"createdAt"`
 }
+
+// Retention: delays in days for completed tasks, the task, triage and notes trash and ticked-off list
+// items; 0 = keep for good.
+type Retention struct {
+	DoneTasks   int `json:"doneTasks"`
+	TaskTrash   int `json:"taskTrash"`
+	TriageTrash int `json:"triageTrash"`
+	NoteTrash   int `json:"noteTrash"`
+	ListDone    int `json:"listDone"`
+}