feat(#251): /api/stores router + wiring + schemas Pydantic + tests API
- Schemas camelCase : StoreInfoResponse, StoreResponse, StoreCreate/UpdateRequest, StoreDocEntryResponse
- Router /api/stores : GET (list), POST (create 201), GET/{slug}, PATCH/{slug}, DELETE/{slug} (204)
- Endpoints documents-in-store : GET /{slug}/documents, DELETE /{slug}/documents/{docId}
- Mapping erreurs StoreServiceError → HTTPException via http_status hint
- StoreService étendu : list_documents/remove_document avec injection optionnelle de document_repo (filename humain)
- Wiring lifespan : SqliteStoreRepository + SqliteDocumentStoreLinkRepository + StoreService sur app.state
- include_router(stores_router) après documents/analyses
- Tests API : 18 cas couvrant 200/201/204/404/409/422 + camelCase + cycle complet
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