fix(app): handle desktop deep links in new layout

[anduimagui]

Issue for this PR

Closes #35225

Type of change

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

What does this PR do?

Desktop opencode://open-project?... and opencode://new-session?... links reached Electron, but the redesigned app layout did not consume them because the deep-link listener only lived in the legacy layout.

This PR:

• adds deep-link handling to the redesigned layout
• supports opening and selecting a project from open-project links
• supports optional session navigation for open-project links
• creates a new draft session for new-session links
• extracts the redesigned layout deep-link wiring into useDesktopDeepLinks so layout-new.tsx stays focused on layout shell concerns

How did you verify your code works?

• bun typecheck from packages/app
• Pre-push hook: bun turbo typecheck

Screenshots / recordings

Not included.

Checklist

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

[github-actions]

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Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

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[github-actions]

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