Wire durable delivery outbox: migration, store, and dispatcher config

Companion to the dispatcher-side outbox change: adds the
delivery_attempts table migration, Store.BeginDeliveryAttempt/
CompleteDeliveryAttempt/ReconcileStaleDeliveryAttempts, and wires
ReconcileStaleDeliveryAttempts + Config.Outbox into mavend startup
before the tick loop resumes.

Vikunja #270.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018ghELqYhZNLub2TXGMazqA

cmd/mavend/main.go

@@ -319,6 +319,13 @@ func run(args []string) error {
 		if voiceW != nil {
 			voiceSink = voiceW.voiceSink
 		}
+		// A crashed prior run may have left "pending" delivery attempts (send
+		// may have landed externally, then the process died before recording
+		// it) — reconcile them to "unknown" before the tick loop resumes
+		// sending, so nothing auto-resends into that ambiguity.
+		if _, err := st.ReconcileStaleDeliveryAttempts(context.Background(), time.Now()); err != nil {
+			log.Printf("delivery outbox reconcile: %v", err)
+		}
 		dispatcher = delivery.NewDispatcher(delivery.Config{
 			Ntfy:      ntfy,
 			Telegram:  telegram,
@@ -326,6 +333,7 @@ func run(args []string) error {
 			Ack:       st,
 			Nudges:    st,
 			Reminders: st,
+			Outbox:    st,
 		})
 
 		// tick loop
@@ -475,6 +483,9 @@ func run(args []string) error {
 			if voiceW != nil {
 				voiceSink = voiceW.voiceSink
 			}
+			if _, err := st.ReconcileStaleDeliveryAttempts(context.Background(), time.Now()); err != nil {
+				log.Printf("delivery outbox reconcile: %v", err)
+			}
 			dispatcher = delivery.NewDispatcher(delivery.Config{
 				Ntfy:      ntfy,
 				Telegram:  telegram,
@@ -482,6 +493,7 @@ func run(args []string) error {
 				Ack:       st,
 				Nudges:    st,
 				Reminders: st,
+				Outbox:    st,
 			})
 
 			tickInterval := time.Duration(cfg.TickInterval)