Add note search API

[Clearner1]

Summary

• add POST /v1/notes/search using native Anki queries
• return matching note fields and tags with bounded pagination
• cover tag, embedded-index, ordering, pagination, and empty-result behavior

Why

AIHOT and other trusted AI clients need one read-only endpoint to retrieve cards by tag, content, or an index already embedded in the card.

Validation

• npm run lint
• npm run typecheck
• npm test
• npm run deadcode
• npm run build
• git diff --check