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>

.env.docker.example

@@ -22,11 +22,14 @@ NEXTAUTH_URL="http://localhost:3000"
 NEXTAUTH_SECRET="changethisinproduction"
 
 # =============================================================================
-# REGISTRATION
+# REGISTRATION & ADMIN
 # =============================================================================
 # Set to "false" to disable public registration (default: true)
 # ALLOW_REGISTRATION=true
 
+# Admin email - The first user registering with this email gets ADMIN role (REQUIRED)
+# ADMIN_EMAIL="admin@yourdomain.com"
+
 # =============================================================================
 # POSTGRESQL CONFIGURATION
 # =============================================================================