feat: add server-sent events for logging and activity tracking

- Implemented a custom tracing layer (`AppLogLayer`) to capture log events and broadcast them to SSE clients.
- Created admin routes for streaming server logs and listing recent activity logs.
- Added an activity log repository interface and SQLite implementation for persisting activity events.
- Integrated activity logging into user authentication and channel CRUD operations.
- Developed frontend components for displaying server logs and activity logs in the admin panel.
- Enhanced the video player with a stats overlay for monitoring streaming metrics.

k-tv-backend/domain/src/repositories.rs

@@ -12,6 +12,16 @@ use crate::entities::{Channel, GeneratedSchedule, PlaybackRecord, User};
 use crate::errors::DomainResult;
 use crate::value_objects::{ChannelId, UserId};
 
+/// An in-app activity event stored in the database for the admin log view.
+#[derive(Debug, Clone)]
+pub struct ActivityEvent {
+    pub id: Uuid,
+    pub timestamp: DateTime<Utc>,
+    pub event_type: String,
+    pub detail: String,
+    pub channel_id: Option<Uuid>,
+}
+
 /// Repository port for User persistence
 #[async_trait]
 pub trait UserRepository: Send + Sync {
@@ -71,3 +81,15 @@ pub trait ScheduleRepository: Send + Sync {
 
     async fn save_playback_record(&self, record: &PlaybackRecord) -> DomainResult<()>;
 }
+
+/// Repository port for activity log persistence.
+#[async_trait]
+pub trait ActivityLogRepository: Send + Sync {
+    async fn log(
+        &self,
+        event_type: &str,
+        detail: &str,
+        channel_id: Option<Uuid>,
+    ) -> DomainResult<()>;
+    async fn recent(&self, limit: u32) -> DomainResult<Vec<ActivityEvent>>;
+}