feat(directive): implement BRIDGE-WP-0004 AccessManagementDirective alignment

- ActorType enum (adm/agt/atm) replaces actor_class string; config validates
  naming convention (adm-*/agt-*/atm-*) with hard ConfigError on mismatch;
  legacy 'human'/'automation' values accepted with DeprecationWarning
- cert_command: pluggable shell string run before each SSH launch; cert written
  to state dir; -i cert appended to SSH command alongside -i key
- TTL-aware cert refresh: parses Valid-to via ssh-keygen -L; pre-emptive restart
  5 min before expiry (no backoff, no attempt increment); CERT_EXPIRING logged
- CertAcquisitionError: cert failures trigger normal backoff/retry loop
- cert_identity: Key ID parsed from cert and recorded in BRIDGE_CONNECTED event
- bridge cert-status: new CLI command; exit 1 on expired cert; --json flag
- 233 tests passing, ruff clean

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/bridge/capabilities.py

@@ -73,6 +73,11 @@ CAPABILITIES: list[Capability] = [
         description="End-to-end tunnel diagnostics via SSH: SSH PID alive + remote port listening",
         required_access_modes=frozenset({"cli", "mcp"}),
     ),
+    Capability(
+        name="bridge_cert_status",
+        description="Show certificate status for tunnels using cert_command mode",
+        required_access_modes=frozenset({"cli"}),
+    ),
 ]
 
 CAPABILITIES_BY_NAME: dict[str, Capability] = {c.name: c for c in CAPABILITIES}