Add docs/solutions/architecture-patterns/bitable-agent-tool-parity-patterns.md
capturing three architecture patterns from U6 (R15a):
- Dual-sync action registration (KTD10): handlers dict + input_schema.enum
- 404-before-403 ownership check (KTD9): prevent existence leak via DELETE
- 409 last-view protection: prevent invalid zero-view table state
Update residual findings with DR-4 (TOCTOU race in delete_view) and DR-5
(_update_field silent type drop) surfaced in final pre-merge ce-code-review
pass. Both P2, neither blocks merge. Documented in the solutions doc under
Known Limitations with concrete fix paths.
chiguyong