feat(mobile): editable activity title for local activities

Adds edits_json column (migration v3) to store user overrides separately
from detail_json so Option A server re-extraction never clobbers them.

- Tap the title in the detail screen to edit (local activities only, shown
  with a ✎ hint). Saves on keyboard dismiss via onEndEditing.
- Cards and search display user_title ?? title.
- Raw upload: user_title sent to server -> sidecar written so web UI shows
  the correct title (server re-extracts from FIT, which has Karoo's title).
- BAS upload: detail.title overridden before sending, no sidecar needed.

mobile/db/index.ts

@@ -35,4 +35,13 @@ export async function migrateDb(db: SQLiteDatabase): Promise<void> {
   } catch {
     // Column already exists — migration already ran, ignore.
   }
+
+  // Migration v3: edits_json stores user overrides (e.g. {"title": "My title"})
+  // kept separate from detail_json so server re-extraction (Option A) never
+  // clobbers user edits.
+  try {
+    await db.execAsync('ALTER TABLE activities ADD COLUMN edits_json TEXT');
+  } catch {
+    // Column already exists — migration already ran, ignore.
+  }
 }