feat: add diagnostics tool for live command output monitoring

- Implemented diagnostics functionality to start, stop, and monitor background check commands.
- Created a DiagnosticsPanel for real-time output display in the UI.
- Added support for auto-detecting default diagnostics commands based on project configuration.
- Introduced run_checks tool to execute project verification commands and report results.
- Enhanced tools-extra with functions to parse AGENTS.md and package.json for check commands.
- Added diff review functionality to visualize changes made in the last turn.
- Implemented tests for diagnostics and run_checks functionalities to ensure reliability.

test/prompt.test.ts

@@ -66,7 +66,7 @@ test('a read-only tool set changes the workflow rules', () => {
 test('a full tool set explains approval and verification', () => {
   const full = systemPrompt({ cwd: '/repo', availableTools: ALL });
   expect(full).toContain('need the user to approve');
-  expect(full).toContain("run the project's build or tests");
+  expect(full).toContain('run_checks');
   expect(full).not.toContain('no tools that change anything');
 });