fix(deps): bump undici to 7.28.0 and dompurify to 3.4.11 (security) (#4304)

* fix(deps): bump undici to 7.28.0 and dompurify to 3.4.11 (security)

Resolves Dependabot alerts on package-lock.json and electron/package-lock.json:

- undici 7.x -> 7.28.0: TLS certificate validation bypass via dropped requestTls in SOCKS5 ProxyAgent (GHSA-vmh5-mc38-953g, HIGH) + cross-user information disclosure via shared-cache whitespace bypass (GHSA-pr7r-676h-xcf6, MEDIUM). Fixed in the root (jsdom transitive) and electron lockfiles.

- dompurify -> 3.4.11: permanent ALLOWED_ATTR pollution via setConfig() bypassing the hook clone-guard (GHSA-cmwh-pvxp-8882, MEDIUM). Bumped the overrides floor from ^3.4.9 to ^3.4.11.

Also bumps node-gyp's transitive undici 6.26.0 -> 6.27.0, clearing the <6.27.0 advisories (WebSocket DoS, Set-Cookie handling) surfaced by npm audit. Lockfile/override-only change; no production source touched.

* ci(quality): exclude dependency manifests/lockfiles from PR test-policy

The PR test-policy gate classifies any changed file under src/, open-sse/, electron/, or bin/ as production code requiring tests. This false-flags lockfile/manifest-only changes (e.g. this Dependabot security bump touching electron/package-lock.json), since a lockfile cannot have a meaningful unit test.

Adds package.json / package-lock.json to EXCLUDED_PATTERNS, consistent with the existing .md/.yaml/.yml exclusions. Real production-code changes remain flagged.

scripts/check/check-pr-test-policy.mjs

@@ -17,6 +17,7 @@ const EXCLUDED_PATTERNS = [
   /\.md$/, // Documentation
   /\.yaml$/, // Config files
   /\.yml$/, // Config files
+  /(?:^|\/)package(?:-lock)?\.json$/, // Dependency manifests/lockfiles (e.g. Dependabot bumps) — not testable code
 ];
 
 function getArg(name, fallbackValue = "") {