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.

bincio/serve/server.py

@@ -636,6 +636,7 @@ async def upload_raw_activity(
     body = await request.json()
     filename_hint: str = body.get("filename") or "activity.fit"
     b64: str = body.get("base64") or ""
+    user_title: Optional[str] = body.get("user_title") or None
     if not b64:
         raise HTTPException(400, "Missing base64 field")
 
@@ -691,6 +692,15 @@ async def upload_raw_activity(
 
         _upsert_index_summary(user_dir, act_id, detail, geojson)
 
+        if user_title:
+            import yaml as _yaml
+            edits_dir = user_dir / "edits"
+            edits_dir.mkdir(parents=True, exist_ok=True)
+            (edits_dir / f"{act_id}.md").write_text(
+                f"---\n{_yaml.dump({'title': user_title}, allow_unicode=True)}---\n",
+                encoding="utf-8",
+            )
+
     except Exception as exc:
         log.warning("upload/raw[%s]: extraction failed: %s", user.handle, exc)
         raise HTTPException(422, f"Could not extract activity: {exc}") from exc