fix(security): close MEDIUM ASVS findings — JWT pinning, SSE tickets, SSRF, mTLS pin, rate limits + correctness bugs

Auth (V2.1.1/V3.1.2, V2.1.3, V3.1.1):
- Pin JWT iss/aud/typ at mint and require+verify them at decode; revocation
  (jti denylist + tokens_valid_from) still enforced.
- Change-password now requires min_length=12.
- SSE auth moves off JWT-in-URL to a single-use 60s opaque ticket
  (POST /auth/sse-ticket); raw JWT in query no longer authenticates a stream.
  Removed dead fail-open get_stream_user helper.

Egress (V5.1.1, V9.1.1/V14.1.3):
- Webhook delivery + CRUD reject SSRF destinations (private/loopback/link-local/
  metadata, IPv4-mapped, multi-A-record) via resolved-IP validation, pin to the
  vetted IP, and never auto-follow redirects. Opt-out via DECNET_WEBHOOK_ALLOW_PRIVATE.
- UpdaterClient pins the worker leaf cert SHA-256 against the stored per-host
  fingerprint (fail closed on missing/mismatch); DECNET_VERIFY_HOSTNAME now
  defaults True.

Hardening (V13.1.3, V4.1.4, V13.1.2):
- Rate-limit change-password (5/min), enroll-bundle (10/min), webhook-create
  (20/min), host-delete (20/min) via the existing slowapi limiter.
- Correct false 'global auth middleware' comment; document enroll-bundle proxy
  trust.

Correctness (BUG-7..11):
- BUG-7 unbound bus in finally; BUG-8 apply_ceiling clamps to min(base,ceiling);
  BUG-9 commit before emit; BUG-10 multi-actor rearm for sub-threshold identities;
  BUG-11 normalize naive timestamps to UTC.

Already-closed (no change): V14.1.1, V2.1.2/V3.1.3, V5.1.2. Tests added for
every fix; unanimous adversarial review.

decnet/swarm/client.py

@@ -112,11 +112,11 @@ class AgentClient:
         """Either pass a SwarmHost dict, or explicit address/port.
 
         ``verify_hostname`` defers to ``DECNET_VERIFY_HOSTNAME`` when the
-        caller doesn't pass an explicit value — production deploys flip
-        the env var on so the worker's cert SAN must match the address
-        the master connects to, on top of the existing CA + fingerprint
-        pin. Defaults to False so dev/test enrollments with mismatched
-        SANs keep working unchanged.
+        caller doesn't pass an explicit value — the worker's cert SAN must
+        match the address the master connects to, on top of the existing CA
+        + fingerprint pin. Defaults to True; operators opt out explicitly
+        via ``DECNET_VERIFY_HOSTNAME=false`` for dev/test enrollments with
+        mismatched SANs.
         """
         if verify_hostname is None:
             from decnet.env import DECNET_VERIFY_HOSTNAME
@@ -155,9 +155,10 @@ class AgentClient:
         )
         ctx.load_verify_locations(cafile=str(self._identity.ca_cert_path))
         ctx.verify_mode = ssl.CERT_REQUIRED
-        # Pin by CA + cert chain, not by DNS — workers enroll with arbitrary
-        # SANs (IPs, hostnames) and we don't want to force operators to keep
-        # those in sync with whatever URL the master happens to use.
+        # Pin by CA + cert chain; hostname verification is on by default
+        # (DECNET_VERIFY_HOSTNAME=true) so the cert SAN must match the
+        # master's connect address.  Operators set the env var to false only
+        # for dev/test enrollments with mismatched SANs.
         ctx.check_hostname = self._verify_hostname
         return httpx.AsyncClient(
             base_url=f"https://{self._address}:{self._port}",