Add search endpoint

[koinsaari]

Background

There is no way for clients to search the library. Jellyfin supports full-text search via SearchTerm on GET /Items.

What to add

• GET /library/search?q=<term>&type=movie|tv&limit=N — returns LibraryListResponse (same shape as paginated browse, no cursor since search results are not paginated).
• Wire to Jellyfin GET /Items?SearchTerm={q}&IncludeItemTypes=Movie,Series&Recursive=true&Limit={limit}.
• type filter is optional — omit to search both movies and TV.
• Add to api/openapi.yaml, run make gen, implement handler and service method.

What stays the same

• LibraryListResponse schema unchanged.
• Existing /library browse endpoint unchanged.
• Auth and error shapes unchanged.