fix(desktop): harden link title transport

[HengYangDS]

Summary

• Gate title URLs and redirects against public-address admission.
• Pin DNS answers through a loopback SOCKS gateway to resist rebinding and direct fallback.
• Fail closed for renderer proxy setup and WebRTC/popup policy failures.
• Add a real Electron hidden BrowserWindow test proving SOCKS routing and an unreachable proxy does not direct-connect.

Verification

• Electron link-title suites: 44 passed.
• UI URL-admission suite: 34 passed.
• npm run typecheck and targeted ESLint passed.

Note

The full Electron project suite has a pre-existing timeout in electron/git-review-ops.test.ts, reproduced unchanged on the untouched local main checkout; it is not included in this PR scope.

[alt-glitch]

This was generated by AI during triage.

Duplicate of #65613 — this later submission keeps the same link-title admission, DNS-pinning, SOCKS-routing, and fail-closed transport implementation; its additional timeout handling and E2E coverage are refinement of that open PR.

[HengYangDS]

Superseded by #65613. Its unique Electron pinned-proxy E2E coverage was transferred to #65613 in a36ab2914; closing this duplicate to keep security review on one canonical branch.