feat: show incomplete Magic Notes todo counts

Magic Notes can now show a default-on incomplete todo badge in the primary
navigation. The badge hides at zero, caps its visual label at 99+ while
retaining the exact accessible count, and refreshes after user or Agent/MCP
note changes.

Platform Features > Magic Notes includes a persistent switch that hides only
the count without changing notes or the Magic Notes entry. Existing settings
migrate with the count enabled.

Release note: 左侧“魔法笔记”入口现在可显示未完成待办数量；可在“平台功能 → 魔法笔记”中关闭，超过 99 项显示“99+”。

src/main/index.ts

@@ -511,7 +511,22 @@ if (hasSingleInstanceLock) {
       | ReturnType<typeof createRerankProvider>
       | undefined
     const startupAssistantDatabase = new AssistantDatabase(
-      join(app.getPath('userData'), 'assistant.sqlite')
+      join(app.getPath('userData'), 'assistant.sqlite'),
+      {
+        onMagicTodosChanged: () => {
+          queueMicrotask(() => {
+            if (
+              mainWindow &&
+              !mainWindow.isDestroyed() &&
+              !mainWindow.webContents.isDestroyed()
+            ) {
+              mainWindow.webContents.send(
+                ipcChannels.magicTodosStatusChanged
+              )
+            }
+          })
+        }
+      }
     )
     assistantDatabase = startupAssistantDatabase
     const goodbuddyConfigService = new GoodBuddyConfigService(