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/infra/src/activity_log_repository/mod.rs

@@ -0,0 +1,5 @@
+#[cfg(feature = "sqlite")]
+mod sqlite;
+
+#[cfg(feature = "sqlite")]
+pub use sqlite::SqliteActivityLogRepository;

k-tv-backend/infra/src/activity_log_repository/sqlite.rs

@@ -0,0 +1,71 @@
+use async_trait::async_trait;
+use chrono::Utc;
+use uuid::Uuid;
+
+use domain::{ActivityEvent, ActivityLogRepository, DomainError, DomainResult};
+
+pub struct SqliteActivityLogRepository {
+    pool: sqlx::SqlitePool,
+}
+
+impl SqliteActivityLogRepository {
+    pub fn new(pool: sqlx::SqlitePool) -> Self {
+        Self { pool }
+    }
+}
+
+#[async_trait]
+impl ActivityLogRepository for SqliteActivityLogRepository {
+    async fn log(
+        &self,
+        event_type: &str,
+        detail: &str,
+        channel_id: Option<Uuid>,
+    ) -> DomainResult<()> {
+        let id = Uuid::new_v4().to_string();
+        let timestamp = Utc::now().to_rfc3339();
+        let channel_id_str = channel_id.map(|id| id.to_string());
+
+        sqlx::query(
+            "INSERT INTO activity_log (id, timestamp, event_type, detail, channel_id) VALUES (?, ?, ?, ?, ?)",
+        )
+        .bind(&id)
+        .bind(&timestamp)
+        .bind(event_type)
+        .bind(detail)
+        .bind(&channel_id_str)
+        .execute(&self.pool)
+        .await
+        .map_err(|e| DomainError::RepositoryError(e.to_string()))?;
+
+        Ok(())
+    }
+
+    async fn recent(&self, limit: u32) -> DomainResult<Vec<ActivityEvent>> {
+        let rows: Vec<(String, String, String, String, Option<String>)> = sqlx::query_as(
+            "SELECT id, timestamp, event_type, detail, channel_id FROM activity_log ORDER BY timestamp DESC LIMIT ?",
+        )
+        .bind(limit)
+        .fetch_all(&self.pool)
+        .await
+        .map_err(|e| DomainError::RepositoryError(e.to_string()))?;
+
+        let events = rows
+            .into_iter()
+            .filter_map(|(id, timestamp, event_type, detail, channel_id)| {
+                let id = Uuid::parse_str(&id).ok()?;
+                let timestamp = timestamp.parse().ok()?;
+                let channel_id = channel_id.and_then(|s| Uuid::parse_str(&s).ok());
+                Some(ActivityEvent {
+                    id,
+                    timestamp,
+                    event_type,
+                    detail,
+                    channel_id,
+                })
+            })
+            .collect();
+
+        Ok(events)
+    }
+}