feat: 8 AI providers, rich text editor, agent notifications, UI contrast & font settings

- Add DeepSeek, OpenRouter, Mistral, Z.AI, LM Studio as AI providers
  with editable model names via Combobox in admin settings
- Fix OpenRouter broken by normalizeProvider bug in config.ts
- Convert agent-created notes from Markdown to HTML (TipTap rich text)
- Add Notification model + in-app notifications for agent results
- Agent notification click opens the created note directly
- Add note count display on notebook and inbox headers
- Fix checklist toggle in card view (persist state via localCheckItems)
- Add checklist creation option in tabs/list view (dropdown on + button)
- Fix image description ENOENT error with HTTP fallback
- Improve UI contrast across all themes (input, border, checkbox visibility)
- Add font family setting (Inter vs System Default) in Appearance settings
- Fix CSS font-sans variable conflict (removed dead Geist references)
- Update README with new features and 8 providers

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

memento-note/app/layout.tsx

@@ -89,7 +89,7 @@ export default async function RootLayout({
         <SessionProviderWrapper>
           <ErrorReporter />
           <DirectionInitializer />
-          <ThemeInitializer theme={userSettings.theme} fontSize={aiSettings.fontSize} />
+          <ThemeInitializer theme={userSettings.theme} fontSize={aiSettings.fontSize} fontFamily={aiSettings.fontFamily} />
           {children}
           <Toaster />
         </SessionProviderWrapper>