reminders: add recurring reminder support

Add cron expression support for recurring reminders using robfig/cron/v3.

Changes:
- Migration #2: ALTER TABLE reminders ADD COLUMN cron TEXT + next_fire_ts INTEGER
- Reminder struct: add Cron and NextFireTs fields
- scanReminder helper extracts full row including nullable cron
- CreateReminder: accept optional cron param, store next_fire_ts = fire_ts
- DueReminders: query on next_fire_ts instead of fire_ts
- RescheduleReminder: new method — parse cron, compute next fire, update
  next_fire_ts or mark fired if no more valid times
- Dispatcher: call RescheduleReminder for cron reminders, MarkReminder for
  one-shots (preserving existing behavior for ID=0 digest skip)
- ReminderCompleter interface: add RescheduleReminder method
- storeAPI adapter: forward RescheduleReminder
- All callers updated: CreateReminder signature includes cron param
- Tests: TestRecurringReminder (store), TestDispatchRecurringReminderReschedules
- Existing tests updated for new signature

internal/delivery/dispatcher.go

@@ -20,11 +20,13 @@ type NudgeRecorder interface {
 	RecordNudge(ctx context.Context, rule, channel, message string, ts time.Time) (int64, error)
 }
 
-// ReminderCompleter — the seam the store implements. a reminder fires once:
-// pending → fired after successful delivery. a failed send does NOT mark the
-// reminder fired (it stays pending; the next tick re-delivers).
+// ReminderCompleter — the seam the store implements. For one-shot reminders:
+// pending → fired after successful delivery. For recurring reminders (with
+// cron): reschedule after successful delivery. A failed send does NOT mark or
+// reschedule it (it stays pending; the next tick re-delivers).
 type ReminderCompleter interface {
 	MarkReminder(ctx context.Context, id int64, status string) error
+	RescheduleReminder(ctx context.Context, id int64, now time.Time) error
 }
 
 // PhrasedNudge — the phraser module's output for a nudge. the phraser (LFM
@@ -184,11 +186,17 @@ func (d *Dispatcher) DispatchReminder(ctx context.Context, pr PhrasedReminder, n
 	}
 	if d.cfg.Reminders != nil && len(out) > 0 {
 		// ID=0 is a synthetic digest reminder; it's not in the DB so
-		// MarkReminder would fail with ErrReminderNotFound. The originals
+		// MarkReminder/RescheduleReminder would fail. The originals
 		// were already marked fired by collapseReminders in gather.go.
 		if rd.Reminder.ID != 0 {
-			if err := d.cfg.Reminders.MarkReminder(ctx, rd.Reminder.ID, "fired"); err != nil {
-				return out, fmt.Errorf("mark reminder fired: %w", err)
+			if rd.Reminder.Cron != "" {
+				if err := d.cfg.Reminders.RescheduleReminder(ctx, rd.Reminder.ID, now); err != nil {
+					return out, fmt.Errorf("reschedule reminder %d: %w", rd.Reminder.ID, err)
+				}
+			} else {
+				if err := d.cfg.Reminders.MarkReminder(ctx, rd.Reminder.ID, "fired"); err != nil {
+					return out, fmt.Errorf("mark reminder fired: %w", err)
+				}
 			}
 		}
 	}

internal/delivery/dispatcher_test.go

@@ -60,7 +60,8 @@ type fakeReminderCompleter struct {
 		id     int64
 		status string
 	}
-	err error
+	rescheduled []int64
+	err         error
 }
 
 func (f *fakeReminderCompleter) MarkReminder(_ context.Context, id int64, status string) error {
@@ -74,6 +75,14 @@ func (f *fakeReminderCompleter) MarkReminder(_ context.Context, id int64, status
 	return nil
 }
 
+func (f *fakeReminderCompleter) RescheduleReminder(_ context.Context, id int64, _ time.Time) error {
+	if f.err != nil {
+		return f.err
+	}
+	f.rescheduled = append(f.rescheduled, id)
+	return nil
+}
+
 type fakeAck struct {
 	acked   map[string]bool
 	lastSent map[string]time.Time
@@ -599,3 +608,30 @@ func TestRepeatUnackedNilTelegramOrAckIsNoOp(t *testing.T) {
 		t.Fatalf("nil telegram/ack: want nil, got %+v", out)
 	}
 }
+
+func TestDispatchRecurringReminderReschedules(t *testing.T) {
+	voice := &fakeSink{}
+	rc := &fakeReminderCompleter{}
+	d := NewDispatcher(Config{Voice: voice, Reminders: rc})
+
+	rd := loop.ReminderDecision{
+		Reminder: store.Reminder{ID: 7, Cron: "0 9 * * *", Status: "pending"},
+		State:    loop.State{Now: refNow(), Presence: store.Present},
+	}
+	out, err := d.DispatchReminder(context.Background(), PhrasedReminder{
+		Decision: rd, Body: "daily standup", Summary: "standup",
+	}, refNow())
+	if err != nil {
+		t.Fatalf("dispatch: %v", err)
+	}
+	if len(out) != 1 {
+		t.Fatalf("want 1 dispatch, got %d", len(out))
+	}
+	// Should RescheduleReminder, not MarkReminder
+	if len(rc.rescheduled) != 1 || rc.rescheduled[0] != 7 {
+		t.Fatalf("want rescheduled 7, got %+v", rc.rescheduled)
+	}
+	if len(rc.marked) != 0 {
+		t.Fatalf("recurring reminder should not be marked fired: %+v", rc.marked)
+	}
+}