Fix Docker OpenClaw HMAC persistence and privacy-core build warnings.

Persist OPENCLAW_HMAC_SECRET to data/openclaw.env so empty Docker env vars no longer block auth after UI bootstrap. Add verify_hmac.py, silence Rust warnings (#423), and document Docker signing (#424).

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/routers/ai_intel.py

@@ -2988,6 +2988,12 @@ def _write_env_value(key: str, value: str) -> None:
     # Also set in current process env so Settings picks it up
     os.environ[key] = value
 
+    try:
+        from services.api_settings import persist_openclaw_env_value
+        persist_openclaw_env_value(key, value)
+    except Exception:
+        pass
+
 
 # ---------------------------------------------------------------------------
 # Agent Identity Management (Ed25519 keypair — used for mesh signing;