fix(notif): set FCM channel on remaining reminder senders (E-OBS)

Add android.notification.channelId to the 4 senders not covered by the earlier batch:
scheduledOutcomesReminder + dailyQuestionReminder + reengagement -> 'reminders';
sendGentleReminderCallable -> 'partner_activity'. Completes E-OBS so backgrounded pushes land on
their proper channels (importance/sound + per-category toggle) instead of fcm_fallback. tsc green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

functions/src/couples/scheduledOutcomesReminder.ts

@@ -123,6 +123,7 @@ async function sendOutcomeReminder(
       title: notification.title,
       body: notification.body,
     },
+    android: { notification: { channelId: 'reminders' } }, // E-OBS
     data: {
       type: 'outcome_reminder',
       coupleId: notification.coupleId,

functions/src/notifications/dailyQuestionReminder.ts

@@ -126,6 +126,7 @@ async function sendReminder(
           title: "Tonight's question is waiting.",
           body: 'Answer together before it expires.',
         },
+        android: { notification: { channelId: 'reminders' } }, // E-OBS
         data: {
           type: 'daily_question_reminder',
           couple_id: coupleId,

functions/src/notifications/reengagement.ts

@@ -96,6 +96,7 @@ async function sendNudge(
           title: "It's been a while.",
           body: "Tonight's question is a good reason to reconnect.",
         },
+        android: { notification: { channelId: 'reminders' } }, // E-OBS
         data: {
           type: 'reengagement',
           couple_id: coupleId,

functions/src/notifications/sendGentleReminderCallable.ts

@@ -169,6 +169,7 @@ export const sendGentleReminderCallable = functions.https.onCall(async (_data, c
             title: 'Your partner is thinking about you.',
             body: "They left tonight's question open. Answer when you're ready.",
           },
+          android: { notification: { channelId: 'partner_activity' } }, // E-OBS
           data: {
             type: 'gentle_reminder',
             couple_id: coupleId,