feat: add GitHub PR list and context APIs

Add PRs list API with pagination
Provide PR context API with optional diff
Integrate PR picker in session UI

packages/desktop/src-tauri/src/main.rs

@@ -47,6 +47,7 @@ use commands::logs::fetch_desktop_logs;
 use commands::github::{
     github_auth_complete, github_auth_disconnect, github_auth_start, github_auth_status, github_me,
     github_issue_comments, github_issue_get, github_issues_list,
+    github_pr_context, github_prs_list,
     github_pr_create, github_pr_merge, github_pr_ready, github_pr_status,
 };
 use commands::notifications::desktop_notify;
@@ -907,6 +908,8 @@ fn main() {
             github_pr_create,
             github_pr_merge,
             github_pr_ready,
+            github_prs_list,
+            github_pr_context,
             github_issues_list,
             github_issue_get,
             github_issue_comments,