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>

tests/conftest.py

@@ -23,10 +23,10 @@ VALID_CONFIG = textwrap.dedent("""\
         local_port: 8000
         ssh_user: ubuntu
         ssh_key: ~/.ssh/id_ops
-        actor: operator.bernd
+        actor: adm-bernd
     actors:
-      operator.bernd:
-        class: human
+      adm-bernd:
+        class: adm
         description: Bernd
 """)
 
@@ -38,10 +38,10 @@ VALID_CONFIG_WITH_CATALOG = textwrap.dedent("""\
         local_port: 8000
         ssh_user: ubuntu
         ssh_key: ~/.ssh/id_ops
-        actor: operator.bernd
+        actor: adm-bernd
     actors:
-      operator.bernd:
-        class: human
+      adm-bernd:
+        class: adm
         description: Bernd
     catalog_path: {catalog_path}
 """)