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/web/db/models/auth.py

@@ -50,7 +50,18 @@ class LoginRequest(BaseModel):
 
 class ChangePasswordRequest(BaseModel):
     old_password: str = PydanticField(..., max_length=72)
-    new_password: str = PydanticField(..., max_length=72)
+    # min_length=12 aligns with the DECNET_ADMIN_PASSWORD >=12 policy. The
+    # forced first-login flow routes through /auth/change-password, so without a
+    # floor a seeded admin could clear must_change_password with a 1-char secret.
+    new_password: str = PydanticField(..., min_length=12, max_length=72)
+
+
+class SSETicketResponse(BaseModel):
+    """Single-use, short-lived opaque ticket the dashboard exchanges its header
+    JWT for, then passes to an SSE endpoint as ?ticket= (EventSource cannot set
+    an Authorization header). See decnet.web.dependencies SSE ticket store."""
+    ticket: str
+    expires_in: int
 
 
 # --- Configuration Models ---