Add GitHub integration for PRs, issues and AI PR description (#205)

* feat: integrate GitHub OAuth device flow across runtimes

Add GitHub OAuth device flow endpoints across runtimes
Introduce GitHubSettings UI panel and sidebar entry
Persist GitHub auth state in per-runtime storage

* feat: add GitHub PR status and PR description generation

Show PR status for the current branch in the Git view
Generate a pull request description from the diff between base and head
Expose prStatus, prCreate, and prMerge APIs in web and desktop clients

* feat: add GitHub PR ready for review

Add API to mark pull requests as ready for review
Show a Ready button for draft PRs and reflect status in UI
Handle token expiration and GraphQL errors when marking ready

packages/web/server/lib/github-octokit.js

@@ -0,0 +1,10 @@
+import { Octokit } from '@octokit/rest';
+import { getGitHubAuth } from './github-auth.js';
+
+export function getOctokitOrNull() {
+  const auth = getGitHubAuth();
+  if (!auth?.accessToken) {
+    return null;
+  }
+  return new Octokit({ auth: auth.accessToken });
+}