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/renderer/src/SettingsPanel.tsx

@@ -185,6 +185,9 @@ type SettingsPanelProps = {
   onAppearanceThemeChange?: (theme: AppearanceTheme) => void
   magicNotesEnabled?: boolean
   onMagicNotesEnabledChange?: (enabled: boolean) => void
+  onMagicNotesShowIncompleteTodoCountChange?: (
+    enabled: boolean
+  ) => void
   onShortcutSettingsChanged?: (
     snapshot: GlobalShortcutSettingsSnapshot
   ) => void
@@ -542,6 +545,7 @@ export function SettingsPanel({
   onAppearanceThemeChange = () => {},
   magicNotesEnabled = false,
   onMagicNotesEnabledChange = () => {},
+  onMagicNotesShowIncompleteTodoCountChange = () => {},
   onShortcutSettingsChanged = () => {},
   onLeaveRequestReady = () => {}
 }: SettingsPanelProps): React.JSX.Element | null {
@@ -1857,6 +1861,9 @@ export function SettingsPanel({
             <PlatformFeaturesSettingsSection
               onDirtyChange={setPlatformFeaturesDirty}
               onMagicNotesEnabledChange={onMagicNotesEnabledChange}
+              onMagicNotesShowIncompleteTodoCountChange={
+                onMagicNotesShowIncompleteTodoCountChange
+              }
               onNotify={onNotify}
               onShortcutSettingsChanged={onShortcutSettingsChanged}
             />