Bulk import/export of story cards (AI Dungeon world-info format)

Add GET /api/story-cards/export and POST /api/story-cards/import for a
scenario or adventure, using the AI Dungeon world-info array shape
(keys/value/type/title/description/useForCharacterCreation) mapped to our
columns. Import accepts a bare array or {cards|storyCards|worldInfo:[...]},
enforces the per-owner cap (existing + incoming) and import rate limit.
Export/Import buttons added to the scenario editor and the in-play Plot
panel.

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

frontend/src/api.js

@@ -127,6 +127,10 @@ export const api = {
   createStoryCard: (data) => request('/story-cards', { method: 'POST', body: JSON.stringify(data) }),
   updateStoryCard: (id, data) => request(`/story-cards/${id}`, { method: 'PATCH', body: JSON.stringify(data) }),
   deleteStoryCard: (id) => request(`/story-cards/${id}`, { method: 'DELETE' }),
+  // Bulk import/export in AI Dungeon world-info format. `owner` is
+  // { scenario_id } or { adventure_id }.
+  exportStoryCards: (owner) => request(`/story-cards/export?${new URLSearchParams(owner)}`),
+  importStoryCards: (payload) => request('/story-cards/import', { method: 'POST', body: JSON.stringify(payload) }),
 
   // Debug
   getDebugRequests: () => request('/debug/requests'),