backend: GDPR export + retention cleanups + worker metrics (BE-1/2/3)

BE-3 observability: expose the worker's Prometheus metrics on :6060/metrics
(apns/fcm/asynq histograms + a new cache_ops_total counter were recorded all
along but never scraped — which is why those dashboard panels read empty); add
the worker containerPort, the vmagent worker scrape job, and two additive
NetworkPolicies. Instrument cache Get/Set hit/miss.

BE-2 retention: three periodic Asynq cleanup crons mirroring the reminder-log
cleanup — notifications (90d), webhook dedup log (180d), audit_log (365d).

BE-1 GDPR data export: POST /api/auth/export/ enqueues a low-priority Asynq job
that gathers all of the user's data (owned residences + their tasks/contractors/
documents/share-codes, plus profile/notifications/prefs/push-tokens/subscription/
audit log), zips one JSON file per category, and emails it as an attachment.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/worker/enqueuer.go

@@ -12,11 +12,17 @@ type Enqueuer interface {
 	EnqueuePasswordResetEmail(to, firstName, code, resetToken string) error
 	EnqueuePasswordChangedEmail(to, firstName string) error
 	EnqueueTaskCompletedNotification(taskID, completionID uint) error
+	EnqueueDataExport(userID uint) error
 }
 
 // Verify TaskClient satisfies the interface at compile time.
 var _ Enqueuer = (*TaskClient)(nil)
 
+// BuildDataExportPayload marshals a DataExportPayload to JSON bytes.
+func BuildDataExportPayload(userID uint) ([]byte, error) {
+	return json.Marshal(DataExportPayload{UserID: userID})
+}
+
 // BuildWelcomeEmailPayload marshals a WelcomeEmailPayload to JSON bytes.
 func BuildWelcomeEmailPayload(to, firstName, code string) ([]byte, error) {
 	return json.Marshal(WelcomeEmailPayload{