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/state.rs

@@ -8,11 +8,14 @@ use axum_extra::extract::cookie::Key;
 use infra::auth::jwt::{JwtConfig, JwtValidator};
 #[cfg(feature = "auth-oidc")]
 use infra::auth::oidc::OidcService;
-use std::sync::Arc;
+use std::collections::VecDeque;
+use std::sync::{Arc, Mutex};
+use tokio::sync::broadcast;
 
 use crate::config::Config;
 use crate::events::EventBus;
-use domain::{ChannelService, ScheduleEngineService, UserService};
+use crate::log_layer::LogLine;
+use domain::{ActivityLogRepository, ChannelService, ScheduleEngineService, UserService};
 
 #[derive(Clone)]
 pub struct AppState {
@@ -27,6 +30,12 @@ pub struct AppState {
     pub jwt_validator: Option<Arc<JwtValidator>>,
     pub config: Arc<Config>,
     pub event_tx: EventBus,
+    /// Broadcast channel for streaming log lines to SSE clients.
+    pub log_tx: broadcast::Sender<LogLine>,
+    /// Ring buffer of recent log lines sent to new SSE clients on connect.
+    pub log_history: Arc<Mutex<VecDeque<LogLine>>>,
+    /// Repository for persisted in-app activity events.
+    pub activity_log_repo: Arc<dyn ActivityLogRepository>,
     /// Index for the local-files provider, used by the rescan route.
     #[cfg(feature = "local-files")]
     pub local_index: Option<Arc<infra::LocalIndex>>,
@@ -46,6 +55,9 @@ impl AppState {
         provider_registry: Arc<infra::ProviderRegistry>,
         config: Config,
         event_tx: EventBus,
+        log_tx: broadcast::Sender<LogLine>,
+        log_history: Arc<Mutex<VecDeque<LogLine>>>,
+        activity_log_repo: Arc<dyn ActivityLogRepository>,
     ) -> anyhow::Result<Self> {
         let cookie_key = Key::derive_from(config.cookie_secret.as_bytes());
 
@@ -118,6 +130,9 @@ impl AppState {
             jwt_validator,
             config: Arc::new(config),
             event_tx,
+            log_tx,
+            log_history,
+            activity_log_repo,
             #[cfg(feature = "local-files")]
             local_index: None,
             #[cfg(feature = "local-files")]