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/config/config.go

@@ -54,6 +54,9 @@ type Config struct {
 	// Legal notices (Impressum, Datenschutz): an external URL and/or Markdown text, shown even before login
 	Legal LegalTexts
 
+	// RetentionAllowNever: RETENTION_ALLOW_NEVER=true/false fixes whether people may keep finished and
+	// deleted things for good; unset (nil) leaves it to the system settings
+	RetentionAllowNever *bool
 	// Speech recognition, configured only by environment (STT_*)
 	Speech SpeechConfig
 
@@ -254,6 +257,7 @@ func Load() *Config {
 		DemoMode:                demoMode,
 		DemoResetMinutes:        demoResetMinutes(),
 		TrustedProxies:          getEnv("TRUSTED_PROXIES", "private"),
+		RetentionAllowNever:     envBoolPtr("RETENTION_ALLOW_NEVER"),
 		DisableLoginProtection:  strings.ToLower(getEnv("LOGIN_PROTECTION", "true")) == "false",
 		SMTPHost:                smtpHost,
 		SMTPPort:                smtpPort,
@@ -369,3 +373,16 @@ func boolEnvOrEmpty(key string) string {
 	}
 	return ""
 }
+
+// envBoolPtr reads true/false; nil when unset or anything else.
+func envBoolPtr(key string) *bool {
+	switch strings.ToLower(strings.TrimSpace(os.Getenv(key))) {
+	case "true", "1", "yes":
+		v := true
+		return &v
+	case "false", "0", "no":
+		v := false
+		return &v
+	}
+	return nil
+}