fix(security): close LOW ASVS findings — env bypass, SSE/deployment authz, CN fail-close, password byte-limit, exception leaks, BUG-12..16

Auth/session (V2.1.7, V4.1.5, V4.1.6, V2.1.4/V2.1.5):
- env secret validation no longer bypassed by attacker-injectable PYTEST* env;
  gated on explicit DECNET_TESTING=1 (set only in conftest).
- must_change_password now enforced on the SSE header-JWT path, not just ticket mint.
- GET /system/deployment-mode requires viewer auth (was leaking role + topology size).
- CreateUser/ResetUser passwords min_length=12; passwords >72 bytes rejected
  explicitly instead of bcrypt silently truncating.

Swarm ingestion (V9.1.3, BUG-16):
- Log listener hard-rejects peers with unparseable/empty cert CN (fail closed,
  ingests nothing) instead of tagging 'unknown'.
- Shutdown handlers no longer swallow real errors (narrowed to CancelledError).

Info leakage (V7.1.2, V14.1.2):
- Exception text sanitized on swarm-update, health, tarpit, realism, file-drop,
  blank-topology endpoints (raw tc/docker stderr, DB/Docker errors logged
  server-side, generic detail returned). pyproject license corrected to AGPL-3.0.

Correctness (BUG-12..16):
- BUG-12 atomic credential upsert (UNIQUE constraint + IntegrityError retry,
  consistent principal_key canonicalization).
- BUG-13 rule-tail watermark uses >= with seen-id dedup (no same-second drop).
- BUG-14 worker wake cleared before wait (no lost wake during tick).
- BUG-15 intel gather tolerates an unexpected provider raise.
- BUG-16 see above.

Already-closed (verified, no change): V2.1.6, V5.1.3, V9.1.2. Accept-risk +
documented: V2.1.8 cache window, V3.1.3 idle timeout. Tests added for every fix;
unanimous adversarial review after two refute-fix rounds.

tests/api/fleet/test_deploy_automode.py

@@ -190,3 +190,15 @@ async def test_deployment_mode_endpoint(client, auth_token, monkeypatch):
     assert body["role"] == "master"
     assert body["mode"] == "unihost"
     assert body["swarm_host_count"] == 0
+
+
+@pytest.mark.anyio
+async def test_deployment_mode_endpoint_requires_auth(client):
+    # V4.1.6: the response leaks host role + enrolled-worker count, so the
+    # endpoint must not be reachable without a valid viewer/admin JWT. The
+    # dashboard only ever calls it from inside the post-login app shell.
+    resp = await client.get("/api/v1/system/deployment-mode")
+    assert resp.status_code == 401
+    # Body must not leak the recon fields on the unauthenticated path.
+    assert "role" not in resp.text
+    assert "swarm_host_count" not in resp.text