fix(chat): play local media paths in markdown

[IgnoreMeBut]

Summary

• normalize sandbox:, file://, POSIX, and Windows absolute media paths through the existing chat-media://local protocol
• return a ready-to-use deliver_markdown link after a successful VideoStudio export
• keep relative paths and remote URLs unchanged; the existing protocol extension, size, and SVG safety gates remain in force

Source review

This ports the shared Orkas fix from b0fb8cf69 after an open-source boundary review. The private regression document was excluded, release-only generated-provider references were not copied, and the original fix author is preserved on the commit.

A negative control against origin/main reproduced three failures: sandbox media remained unservable, the normalizer was absent, and VideoStudio omitted the delivery link.

Testing

• node scripts/run-tests.mjs run test/renderer/utils-autolink.test.ts test/main/model/core-agent/video-studio-state-tool.test.ts (103 passed)
• related media/chat suite (248 passed)
• npm run typecheck
• node --check src/renderer/modules/utils.js
• npm run smoke
• npm test -- --reporter=dot (5855 passed, 15 skipped; 3 unrelated baseline failures in builtin marketplace tombstone and bundled runtime path cases)
• OSS sync postcheck reported zero forbidden symbols, provider/API changed-file violations, and orphan imports for this diff; the repository-wide check remains blocked by 11 pre-existing main-branch sync violations