search: corpus fingerprint excludes title/body, can serve stale cache

[Ariestar]

CodeRabbit finding on PR #80 (no-unwrap), src/commands/browse/picker.rs.

search_corpus_fingerprint hashes only record.work_ref.whole() per hydrated record. If searchable content changes without the ref changing (e.g. re-hydration updates a session's search_title, WorkRecord.title, or body records), the cached WorkspaceSearchIndex stays current-looking and search returns stale results.

Suggested direction: fold every indexed/searchable field (metadata, titles, body content) into the fingerprint, not just the refs.