Hydrate the feed from /api/activities (currently seed-only)

Problem

The tb store inits activities from seedActivities and never fetches GET /api/activities, so the feed/profile never show real runs (even after the recorder persists one). A hydrateTerritoriesFromApi/hydrateTrailsFromApi pattern exists but there's no activities equivalent.

Acceptance

• Add hydrateActivitiesFromApi + a useActivityCatalog composable; call it from the layout.
• Feed/profile render DB activities; fall back to seed when empty.

Done: ActivityIndexAction joins owner/trail names + title; useActivityCatalog + hydrateActivitiesFromApi wired in the default layout; seed-game-world seeds 12 feed activities. Commit c9007b4.