Five more resources following clients.rs's template exactly: the
same list/get/create/update/delete shape, including the
fetch-merge-write pattern for update. quotes.rs is otherwise
identical to invoices.rs since Quote is a type alias for Invoice in
the SDK (same table, distinguished by entity_type upstream).
Verified against a live local server: full create/list/get/update/
delete round trip for all six resources, confirming update preserves
fields the caller didn't mention.
Also adds CHANGELOG.md (Keep a Changelog format, matching the SDK's)
and updates README/CLAUDE.md's resource counts.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
