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/queries.ts

@@ -13,11 +13,13 @@ export type ActivityRow = {
   synced_at: number | null;
   origin: 'local' | 'remote';
   created_at: number;
+  edits_json: string | null;
 };
 
 export type ActivitySummary = {
   id: string;
   title: string;
+  user_title: string | null;  // from edits_json; takes display priority over title
   sport: string;
   started_at: string;
   distance_m: number | null;
@@ -34,20 +36,11 @@ const PAGE_SIZE = 50;
 export function useActivities(searchQuery = '', limit = PAGE_SIZE): ActivitySummary[] {
   const db = useSQLiteContext();
   const like = `%${searchQuery}%`;
-  const rows = db.getAllSync<{
-    id: string;
-    origin: 'local' | 'remote';
-    synced_at: number | null;
-    title: string;
-    sport: string;
-    started_at: string;
-    distance_m: number | null;
-    duration_s: number | null;
-    elevation_gain_m: number | null;
-  }>(`
+  const rows = db.getAllSync<ActivitySummary>(`
     SELECT
       id, origin, synced_at,
       json_extract(detail_json, '$.title')            AS title,
+      json_extract(edits_json,  '$.title')            AS user_title,
       json_extract(detail_json, '$.sport')            AS sport,
       json_extract(detail_json, '$.started_at')       AS started_at,
       json_extract(detail_json, '$.distance_m')       AS distance_m,
@@ -93,6 +86,7 @@ export function useFilteredActivities(filter: ActivityFilter, limit = PAGE_SIZE)
     SELECT
       id, origin, synced_at,
       json_extract(detail_json, '$.title')            AS title,
+      json_extract(edits_json,  '$.title')            AS user_title,
       json_extract(detail_json, '$.sport')            AS sport,
       json_extract(detail_json, '$.started_at')       AS started_at,
       json_extract(detail_json, '$.distance_m')       AS distance_m,
@@ -194,6 +188,19 @@ export async function deleteActivity(
   return row?.original_path ?? null;
 }
 
+export async function setActivityTitle(
+  db: ReturnType<typeof useSQLiteContext>,
+  id: string,
+  title: string,
+): Promise<void> {
+  await db.runAsync(
+    `UPDATE activities
+     SET edits_json = json_set(COALESCE(edits_json, '{}'), '$.title', ?)
+     WHERE id = ?`,
+    [title, id],
+  );
+}
+
 export async function deleteActivities(
   db: ReturnType<typeof useSQLiteContext>,
   ids: string[],