Accumulate OpenCode settings restarts behind Apply & Restart

Defer OpenCode reloads after settings mutations, track pending changes,
and expose a top-right Apply & Restart OpenCode action with a counter so
sessions stay available until the user explicitly applies.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

packages/web/server/lib/opencode/config-mutation-response.test.js

@@ -0,0 +1,27 @@
+import { describe, expect, test } from 'bun:test';
+
+import {
+  buildDeferredRestartResponse,
+  buildExternalManualRestartResponse,
+} from './config-mutation-response.js';
+
+describe('config mutation response helpers', () => {
+  test('buildDeferredRestartResponse marks restart as deferred', () => {
+    expect(buildDeferredRestartResponse('Saved. Restart OpenCode to apply.')).toEqual({
+      success: true,
+      requiresReload: false,
+      requiresRestart: true,
+      restartDeferred: true,
+      message: 'Saved. Restart OpenCode to apply.',
+    });
+  });
+
+  test('buildExternalManualRestartResponse asks for external restart', () => {
+    expect(buildExternalManualRestartResponse('Restart your server.')).toEqual({
+      success: true,
+      requiresReload: false,
+      requiresManualRestart: true,
+      message: 'Restart your server.',
+    });
+  });
+});