fix(p0): HTTP trust boundary + audit SQL redact

[tangyf07]

Summary

• P0-5 HTTP trust boundary: serve locks database / policy / catalog / environment at startup; request bodies may only supply sql / actor / model_id / prompt_summary. Overrides of policy / catalog / database / db_path / environment return 400 trust_boundary_violation.
• Non-loopback binds (including 0.0.0.0 / ::) require --auth-token or SQL_WRITE_GATE_HTTP_TOKEN; all-interfaces without auth is refused at startup.
• Audit SQL: default literal redaction via SQL_WRITE_GATE_AUDIT_SQL_MODE=redact|hash|plain.
• sqlglot compatibility ceiling: >=25,<31.
• CI: Python 3.11 + 3.12 matrix; live Postgres/MySQL integration remains 3.12-only.
• README: replace 「HTTP binding is not server-locked」 with real serve lock guarantee.

Test plan

• pytest tests/test_p0_http_trust_boundary.py tests/test_audit.py tests/test_v110.py tests/test_readme.py (green locally on tangyf)
• CI matrix 3.11/3.12 on this PR

Notes

• Tip: d83508d
• Local origin fetch/push over HTTPS:443 from tangyf failed (connection reset); branch pushed via alternate path (box + git bundle). No force-push / no merge.