Add per-adventure "Sync from library" for scripts

Adventure scripts are frozen snapshots taken at creation. Add an opt-in
way to pull the latest library code into a live adventure:

- AdventureScript.source_script_id links a copy to its library Script
  (migration 24; set at adventure creation)
- list endpoint flags out_of_date by diffing copy vs library
- POST /adventures/{id}/scripts/{sid}/sync overwrites the copy's code,
  preserving enabled/position/script_state
- legacy copies with no link fall back to a name match, then adopt the link
- Play page shows a Sync button only when a copy differs from its library

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TEpWMjnfPqzZ13nPMoGhs5

frontend/src/api.js

@@ -109,6 +109,8 @@ export const api = {
   listAdventureScripts: (advId) => request(`/adventures/${advId}/scripts`),
   updateAdventureScript: (advId, scriptId, data) =>
     request(`/adventures/${advId}/scripts/${scriptId}`, { method: 'PATCH', body: JSON.stringify(data) }),
+  syncAdventureScript: (advId, scriptId) =>
+    request(`/adventures/${advId}/scripts/${scriptId}/sync`, { method: 'POST' }),
 
   // Scripts
   listScripts: () => request('/scripts'),