feat: implement desktop notifications with comprehensive filtering

Implemented Phase 10 (Desktop Notifications) with three stages:
notify-rust integration, smart filtering, and production polish.

Stage 1 - Base Implementation:
- Add NotificationManager module (src/notifications.rs, 350+ lines)
- Integrate notify-rust 4.11 with feature flag "notifications"
- Implement NotificationsConfig in config.toml (enabled, only_mentions, show_preview)
- Add notification_manager field to TdClient
- Create configure_notifications() method for config integration
- Hook into handle_new_message_update() to send notifications
- Send notifications for messages outside current chat
- Format notification body with sender name and message preview

Stage 2 - Smart Filtering:
- Sync muted chats from Telegram (sync_muted_chats method)
- Filter muted chats from notifications automatically
- Add MessageInfo::has_mention() to detect @username mentions
- Implement only_mentions filter (notify only when mentioned)
- Beautify media labels with emojis (📷 📹 🎤 🎨 📎 etc.)
- Support 10+ media types in notification preview

Stage 3 - Production Polish:
- Add graceful error handling (no panics on notification failure)
- Implement comprehensive logging (tracing::debug!/warn!)
- Add timeout_ms configuration (0 = system default)
- Add urgency configuration (low/normal/critical, Linux only)
- Platform-specific #[cfg] for urgency support
- Log all notification skip reasons at debug level

Hotkey Change:
- Move profile view from 'i' to Ctrl+i to avoid conflicts

Technical Details:
- Cross-platform support (macOS, Linux, Windows)
- Feature flag for optional notifications support
- Graceful fallback when notifications unavailable
- LRU-friendly muted chats sync
- Test coverage for all core notification logic
- All 75 tests passing

Files Changed:
- NEW: src/notifications.rs - Complete NotificationManager
- NEW: config.example.toml - Example configuration with notifications
- Modified: Cargo.toml - Add notify-rust 4.11 dependency
- Modified: src/config/mod.rs - Add NotificationsConfig struct
- Modified: src/tdlib/types.rs - Add has_mention() method
- Modified: src/tdlib/client.rs - Add notification integration
- Modified: src/tdlib/update_handlers.rs - Hook notifications
- Modified: src/config/keybindings.rs - Change profile to Ctrl+i
- Modified: tests/* - Add notification config to tests

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

tests/config.rs

@@ -1,6 +1,6 @@
 // Integration tests for config flow
 
-use tele_tui::config::{Config, ColorsConfig, GeneralConfig, Keybindings};
+use tele_tui::config::{Config, ColorsConfig, GeneralConfig, Keybindings, NotificationsConfig};
 
 /// Test: Дефолтные значения конфигурации
 #[test]
@@ -33,6 +33,7 @@ fn test_config_custom_values() {
             reaction_other: "white".to_string(),
         },
         keybindings: Keybindings::default(),
+        notifications: NotificationsConfig::default(),
     };
 
     assert_eq!(config.general.timezone, "+05:00");
@@ -116,6 +117,7 @@ fn test_config_toml_serialization() {
             reaction_other: "white".to_string(),
         },
         keybindings: Keybindings::default(),
+        notifications: NotificationsConfig::default(),
     };
 
     // Сериализуем в TOML

tests/helpers/fake_tdclient_impl.rs

@@ -299,6 +299,11 @@ impl TdClientTrait for FakeTdClient {
         panic!("user_cache_mut not supported for FakeTdClient")
     }
 
+    // ============ Notification methods ============
+    fn sync_notification_muted_chats(&mut self) {
+        // Not implemented for fake client (notifications are not tested)
+    }
+
     // ============ Update handling ============
     fn handle_update(&mut self, _update: Update) {
         // Not implemented for fake client