Upgrade the eight shipped dependencies carrying advisories

scan_sbom.py reported 50 advisory matches against shipped components, 16 of them
at or above HIGH. This clears all of them: the scan now reports 0 shipped
findings and the gate passes.

  pyjwt             2.12.1  -> 2.13.0
  idna              3.13    -> 3.19
  axios             1.13.2  -> 1.20.0   (29 advisories)
  postcss           8.5.6   -> 8.5.26
  dompurify         3.4.11  -> 3.4.14
  nanoid            3.3.11  -> 3.3.18
  follow-redirects  1.15.11 -> 1.16.0
  form-data         4.0.5   -> 4.0.6

Every one is an in-major bump inside a range the manifests already allowed, so
this is a lockfile refresh rather than a migration. The Python side was compiled
with --upgrade-package for each name so nothing else moved; the diff is two
version lines and their hashes.

nanoid is worth recording: it is transitive under postcss at ^3.3.11, and its
advisories are fixed on both the 3.x and 5.x branches. 3.3.18 is the fix that is
actually reachable.

The declared floors for axios and dompurify were raised to the versions in the
lockfile. They were ^1.6.0 and ^3.4.11, which still nominally admitted the
vulnerable range - npm resolves to the highest match so an install was never
going to pick one, but the manifest should state the minimum safe version rather
than rely on that.

axios 1.20 adds optional proxy-agent support, which pulls https-proxy-agent and
agent-base into the tree. Both are Node-only and neither reaches the browser
bundle; the build was checked for them. The main chunk grew 256kB to 271kB
(85.7kB to 90.5kB gzipped) from the rest of the axios delta.

The PyJWT entry in the allowlist was removed rather than kept. It stopped
matching the moment the upgrade landed, and an allowlist that accumulates
entries for advisories that no longer apply is one nobody rereads. The reasoning
is preserved as the worked example in docs/DEPENDENCY-SECURITY.md.

Verified: full suite 2161 passed, frontend 273 passed, build clean,
npm audit --omit=dev reports 0 vulnerabilities.

scripts/vulnerability-allowlist.json

@@ -8,20 +8,16 @@
     "An entry needs an id, a reason that names the precondition that is",
     "absent, who accepted it, and when. 'reviewuntil' is when the reasoning",
     "should be checked again - a reason stops being true when the code that",
-    "made it true changes.",
+    "made it true changes, and 'invalidatedby' should say what that change",
+    "would be.",
+    "",
+    "Currently EMPTY, which is the state to aim for. The one entry this file",
+    "has held so far - a PyJWT algorithm-confusion advisory that needed a",
+    "configuration this application does not use - was removed by upgrading",
+    "PyJWT rather than by keeping the exception.",
     "",
     "Do NOT add an entry to make a build pass. Upgrading the dependency is",
     "almost always cheaper than defending a decision to skip it."
   ],
-  "accepted": [
-    {
-      "id": "GHSA-xgmm-8j9v-c9wx",
-      "component": "pyjwt",
-      "reason": "Needs a verifier configured with BOTH symmetric and asymmetric algorithms and a raw JSON JWK passed as key=. Neither is present: auth goes through flask-jwt-extended with no JWT_ALGORITHM or JWT_DECODE_ALGORITHMS override anywhere in the tree, so it is HS256-only, and the key is the JWT_SECRET_KEY string. Upstream rates the attack complexity High for exactly this reason. Upgrade to pyjwt 2.13.0 anyway at the next dependency bump; this entry only says it is not urgent.",
-      "acceptedby": "DT team, reference site",
-      "accepted": "2026-08-29",
-      "reviewuntil": "2026-11-29",
-      "invalidatedby": "Setting JWT_ALGORITHM or JWT_DECODE_ALGORITHMS to anything asymmetric, or moving to SSO-issued tokens verified against a JWK."
-    }
-  ]
+  "accepted": []
 }