fix: update swagger-ui to 5.29.1 and add SRI hashes

[lbellows]

Fixes #1053 (the SRI and version part; keeps the CDN as discussed there).

• Bumps swagger-ui on /docs from 4.15.5 to 5.29.1, the newest release on cdnjs. npm has 5.33.0, but cdnjs has not published it yet.
• Adds integrity (sha512), crossorigin="anonymous" and referrerpolicy="no-referrer" to the stylesheet and both scripts. cdnjs sends Access-Control-Allow-Origin: *, so the CORS-mode fetch SRI needs works.
• Adds a test that fails if an external <script>/<link> in the page has no hash, so a later version bump can't drop it without anyone noticing.

The hashes match three sources: the cdnjs API, a local sha512 of the served files, and the swagger-ui-dist@5.29.1 npm tarball (byte-identical).

Regression check. I ran master and this branch side by side and loaded /docs in headless Chromium:

	master (4.15.5)	this PR (5.29.1)
operations rendered	42	42
tags	application, message, auth, oidc, client, user, info, plugin	same
security schemes in Authorize dialog	7	same 7
Basic auth → Try it out → GET /current/user	200, admin user	200, admin user
host from swagger?base=	correct	correct
console errors	none (favicon 404s only, pre-existing)	same
390px mobile viewport	no horizontal scroll	same

The Swagger 2.0 spec renders unchanged. 5.x only adds an "OAS 2.0" badge next to the version.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.09%. Comparing base (d02796b) to head (8492a2c).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1060   +/-   ##
=======================================
  Coverage   76.09%   76.09%           
=======================================
  Files          67       67           
  Lines        3619     3619           
=======================================
  Hits         2754     2754           
  Misses        654      654           
  Partials      211      211           

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[jmattheis]

Thanks