The book/topic field was really always a general-purpose tag, and now
that notes can come from more than just books (camera-scanned pages,
free text), "book" was misleading in the UI as well as the code.
Renames files, functions, variables, the API route (/api/books ->
/api/topics), the note payload field, and the cache TTL env var
(BOOK_CACHE_TTL_MS -> TOPIC_CACHE_TTL_MS) for consistency.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01C3DGg1pvmvf81zXs4pk1J7
Notes are saved as markdown pages in a Nextcloud collective via the Collectives OCS API (page metadata/creation) and WebDAV (content read/append), following the same npm-workspaces + session-auth architecture as CityTracker.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NvmYFQSMqs2N3q2zUDNTVn
