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/api/src/dto.rs

@@ -59,6 +59,32 @@ pub struct ConfigResponse {
     pub provider_capabilities: domain::ProviderCapabilities,
 }
 
+// ============================================================================
+// Admin DTOs
+// ============================================================================
+
+/// An activity log entry returned by GET /admin/activity.
+#[derive(Debug, Serialize)]
+pub struct ActivityEventResponse {
+    pub id: Uuid,
+    pub timestamp: DateTime<Utc>,
+    pub event_type: String,
+    pub detail: String,
+    pub channel_id: Option<Uuid>,
+}
+
+impl From<domain::ActivityEvent> for ActivityEventResponse {
+    fn from(e: domain::ActivityEvent) -> Self {
+        Self {
+            id: e.id,
+            timestamp: e.timestamp,
+            event_type: e.event_type,
+            detail: e.detail,
+            channel_id: e.channel_id,
+        }
+    }
+}
+
 // ============================================================================
 // Channel DTOs
 // ============================================================================