* feat(frontend): pin recent chats
* fix(threads): address pin-chat review feedback
- Stop bumping updated_at on metadata-only PATCH (pin/unpin) via a new
update_metadata(touch=False) path so unpinning no longer jumps a chat
to the top of the updated_at-sorted recent list.
- Narrow patchThreadMetadata to a ThreadMetadataPatchResponse matching
the Gateway's actual response (no values/context).
- Namespace the pinned metadata key as deerflow_pinned for consistency
with deerflow_sidecar / deerflow_branch.
- Cover touch/touch=False behavior in repo + router tests; document the
e2e mock's updated_at preservation now mirrors production.
* style(frontend): format thread utils test
* fix(threads): make pinned ordering server-side
* test(frontend): keep infinite-scroll fixture order stable
* test(frontend): stabilize lark reconnect e2e
* docs: clarify thread pin metadata contract
