[FEATURE]: Show GitHub PR review comments inline in the Desktop review panel

[athal7]

Problem

When addressing PR review feedback, you have to context-switch between the
OpenCode desktop app (to see the diff and work on fixes) and GitHub (to read
reviewer comments). There's no way to see what reviewers said next to the
relevant code while you're working on it.

Proposed Feature

Surface GitHub PR review comments inline in the desktop app's review/diff
panel — similar to how GitHub's "Files changed" tab shows reviewer threads
next to the relevant lines of code.

Concretely:

• When a PR is open for the current branch, fetch review comments via the
  GitHub API and overlay them on the diff at the correct file+line positions
• Show commenter, timestamp, and comment body
• Optionally: allow resolving threads from within the app
• Optionally: support suggestion blocks with one-click apply

Relationship to #13918

Issue #13918 requests that OpenCode post inline comments when running in
the GitHub Action context. This is the inverse: reading existing review
comments into the local desktop UI so you can act on them without leaving
the app.

Why This Matters

• Eliminates the context-switch between GitHub and the desktop app during
  review cycles
• Keeps reviewer intent visible right next to the code being fixed
• Opens the door to agent-assisted resolution ("fix all review comments")