feat(desktop): improve Console onboarding

[usrnk1]

Issue for this PR

N/A — WIP follow-up to the Desktop Console authentication flow.

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Improves first-run provider setup in Desktop. OpenCode Console is now the primary path, opens in the browser with an in-app device-code confirmation state, handles cancellation and recovery, and preserves the current draft.

After the first provider connects, Desktop presents that connection's available models before returning to a new session. Console-backed providers are grouped consistently in Settings, and subsequent connections return there with a toast. The Desktop callback contract also carries the originating window ID so a future Console redirect can focus the correct window without treating the deep link as authorization truth.

This is intentionally a draft; more UI polish and the matching Console redirect are still expected.

How did you verify your code works?

• bun turbo typecheck --concurrency=3 (push hook; 35 tasks passed)
• bun typecheck, bun run typecheck:e2e, and bun run test:unit in packages/app (842 passed, 1 skipped)
• Desktop onboarding Playwright suite (14 passed)
• bun typecheck in packages/desktop and packages/ui
• Desktop unit suite: 167 passed, 1 skipped; two unrelated native-browser harness cases failed on existing screenshot ownership / closed-tab assertions
• Manual light, dark, narrow, RTL, browser-return, and multi-window checks

Screenshots / recordings

WIP — screenshots/recording will be attached during follow-up polish.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR