[task] Build desktop PR list and detail panel

[phongndo]

Goal

Add desktop PR list and selected PR detail panels backed by app-server PR data.

Why this matters

PR review and maintainer queue work are central to Nexgit's desktop value. The app should give users a local PR dashboard before adding write actions.

Command/API target

Call github.pr.list and github.pr.view through the typed preload/app-server path.

Depends on

• [task] Add app-server PR list and view methods #9 for PR list/view data.
• [task] Render GitHub workflow dashboard in desktop #14 for desktop dashboard structure.

Out of scope

• Do not implement merge, checkout, or review actions.
• Do not call GitHub directly from renderer code.
• Do not implement checks/review detail panels here.

Definition of done

• Desktop shows PR list and selected PR summary details.
• Branch/base, state, author, labels, and URL are shown where available.
• Loading, empty, no-auth, no-repo, and error states are visible.

Verification

• pnpm desktop:typecheck
• pnpm desktop:build
• Run pnpm desktop:dev and include screenshots or concise manual observations.

[github-actions]

This issue needs a small update before triage:

• Area must be one of Automation, CLI, Core, Desktop, Design, Docs, Protocol, Tests, or TUI so triage automation can route the issue.

Please edit the issue instead of opening a new one.

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Potentially related existing work:

• [task] Build desktop issue list panel #20 [task] Build desktop issue list panel (open)
• [task] Build desktop checks and review panel #22 [task] Build desktop checks and review panel (open)
• [task] Render GitHub workflow dashboard in desktop #14 [task] Render GitHub workflow dashboard in desktop (open)

If one of these is the canonical thread, comment there and a maintainer can close this issue with /duplicate #123; otherwise a maintainer can clear the review with /not-duplicate.