feat: add notifications view and update branding

- Add complete notifications management view with:
  - Service status display (Discord, Telegram)
  - Test notification functionality
  - Service management (delete/disable)
  - Filter settings display (case sensitive/insensitive)
- Update API types to match current backend structure
- Fix NotificationFilters type (remove deprecated fields)
- Update page title from 'Vite + React + TS' to 'Leggen'
- Replace Vite favicon with custom Leggen favicon
- Add notifications tab to main navigation
- Ensure full API compatibility with current backend

frontend/src/types/api.ts

@@ -86,3 +86,42 @@ export interface PaginatedResponse<T> {
   per_page: number;
   total_pages: number;
 }
+
+// Notification types
+export interface DiscordConfig {
+  webhook: string;
+  enabled: boolean;
+}
+
+export interface TelegramConfig {
+  token: string;
+  chat_id: number;
+  enabled: boolean;
+}
+
+export interface NotificationFilters {
+  case_insensitive: string[];
+  case_sensitive?: string[];
+}
+
+export interface NotificationSettings {
+  discord?: DiscordConfig;
+  telegram?: TelegramConfig;
+  filters: NotificationFilters;
+}
+
+export interface NotificationTest {
+  service: string;
+  message?: string;
+}
+
+export interface NotificationService {
+  name: string;
+  enabled: boolean;
+  configured: boolean;
+  active?: boolean;
+}
+
+export interface NotificationServicesResponse {
+  [serviceName: string]: NotificationService;
+}