feat: encrypted-history prompt, incoming-call alerts, message edit, panic button (v1.7.0+11)

P1 key_restore_prompt: offer recovery-key restore right after login
P2 incoming calls: mount overlay in app.dart + detect MSC3401 call.member
   (Element X signalling) — calls were previously invisible
P3 message edit: editMessage/EditMessage + Edit dialog (reactions/delete
   were already wired)
P5 panic button: new feature/panic module — hold-to-send alert text +
   m.location to a configured room; alert sent before geolocation so a
   denied permission never blocks it

All verified end-to-end in headless Chromium against production build.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

lib/features/chat/data/chat_repository.dart

@@ -1,4 +1,4 @@
-// Version: 1.3.0 | Created: 2026-04-01 | Updated: 2026-04-10
+// Version: 1.4.0 | Created: 2026-04-01 | Updated: 2026-07-04
 // Chat repository — bridges Matrix SDK timeline to app domain models.
 // Phase 2 additions: sendFile, sendReaction, redactEvent, reply support.
 
@@ -73,6 +73,17 @@ class ChatRepository {
     await room.sendFileEvent(file);
   }
 
+  /// Replaces the body of an existing text message (m.replace edit).
+  Future<void> editMessage(
+    String roomId,
+    String eventId,
+    String newText,
+  ) async {
+    final room = _getRoom(roomId);
+    if (room == null) return;
+    await room.sendTextEvent(newText, editEventId: eventId);
+  }
+
   /// Sends an emoji reaction to [eventId].
   Future<void> sendReaction(String roomId, String eventId, String emoji) async {
     final room = _getRoom(roomId);