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>

src/tdlib/types.rs

@@ -1,3 +1,4 @@
+use tdlib_rs::enums::TextEntityType;
 use tdlib_rs::types::TextEntity;
 
 use crate::types::{ChatId, MessageId};
@@ -192,6 +193,16 @@ impl MessageInfo {
         self.state.can_be_deleted_for_all_users
     }
 
+    /// Checks if the message contains a mention (@username or user mention)
+    pub fn has_mention(&self) -> bool {
+        self.content.entities.iter().any(|entity| {
+            matches!(
+                entity.r#type,
+                TextEntityType::Mention | TextEntityType::MentionName(_)
+            )
+        })
+    }
+
     pub fn reply_to(&self) -> Option<&ReplyInfo> {
         self.interactions.reply_to.as_ref()
     }
@@ -475,6 +486,39 @@ mod tests {
         assert!(message.can_be_edited());
         assert!(message.can_be_deleted_for_all_users());
     }
+
+    #[test]
+    fn test_message_has_mention() {
+        // Message without mentions
+        let message = MessageBuilder::new(MessageId::new(1))
+            .text("Hello world")
+            .build();
+        assert!(!message.has_mention());
+
+        // Message with @mention
+        let message_with_mention = MessageBuilder::new(MessageId::new(2))
+            .text("Hello @user")
+            .entities(vec![TextEntity {
+                offset: 6,
+                length: 5,
+                r#type: TextEntityType::Mention,
+            }])
+            .build();
+        assert!(message_with_mention.has_mention());
+
+        // Message with MentionName
+        let message_with_mention_name = MessageBuilder::new(MessageId::new(3))
+            .text("Hello John")
+            .entities(vec![TextEntity {
+                offset: 6,
+                length: 4,
+                r#type: TextEntityType::MentionName(
+                    tdlib_rs::types::TextEntityTypeMentionName { user_id: 123 },
+                ),
+            }])
+            .build();
+        assert!(message_with_mention_name.has_mention());
+    }
 }
 
 #[derive(Debug, Clone)]