fix: consolidate media and service worker fixes

[Just-Insane]

Description

Consolidates the media cache, authenticated media rendering, URL preview, and service-worker session handling fixes from the local cleanup work.

Changeset: fix: harden authenticated media and service-worker transport.

This is one domain-sized split from the rebuilt aggregate branch in #25. The aggregate integration branch at ebd4679e8 passed the full quality gate; this split is draft because it depends on shared cleanup from the companion split PRs.

Pre-PR research: origin has related closed/merged media/service-worker PRs #8, #12, #13, #20, #21, #22, #23, and #24, plus aggregate #25. SableClient/Sable and cinnyapp/cinny searches for open media/service-worker overlap returned no open matches. Origin issues are disabled; searched upstream/cinny issues returned no matches to link.

Fixes #

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

Validation: rebuilt integration at ebd4679e8 passed pnpm lint, pnpm fmt:check, pnpm typecheck, pnpm test:run, pnpm knip, and pnpm build. Targeted media/settings/safe-area tests also passed before the aggregate push.

AI disclosure:

• Partially AI assisted (clarify which code was AI assisted and briefly explain what it does).
• Fully AI generated (explain what all the generated code does in moderate detail).
  AI-assisted consolidation and regression cleanup; maintainer should revise this disclosure before merge.

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