feat(plugins): add PluginContext, PluginRegistry, and SettingsStore

- PluginContext: scoped API with crash-safe command wrappers
- PluginRegistry: lifecycle management with graceful init failure
- SettingsStore: plugin-scoped key/value via IPC backend
- Export hooks: pre/post hooks on registry for cross-plugin integration

Amit Haridas

tests/settings-store.test.js

@@ -0,0 +1,34 @@
+const { SettingsStore } = require('../src/plugins/settings-store');
+
+describe('SettingsStore', () => {
+  let store;
+  let data;
+
+  beforeEach(() => {
+    data = {};
+    store = new SettingsStore({
+      get: (key) => data[key],
+      set: (key, value) => { data[key] = value; }
+    });
+  });
+
+  test('get returns value for full key', () => {
+    data['plugins.my-plugin.myKey'] = 'myValue';
+    expect(store.get('plugins.my-plugin.myKey')).toBe('myValue');
+  });
+
+  test('get returns undefined for missing key', () => {
+    expect(store.get('plugins.my-plugin.missing')).toBeUndefined();
+  });
+
+  test('set stores value', () => {
+    store.set('plugins.my-plugin.myKey', 42);
+    expect(data['plugins.my-plugin.myKey']).toBe(42);
+  });
+
+  test('set overwrites existing value', () => {
+    data['plugins.my-plugin.myKey'] = 'old';
+    store.set('plugins.my-plugin.myKey', 'new');
+    expect(data['plugins.my-plugin.myKey']).toBe('new');
+  });
+});