feat(transcoding): add FFmpeg HLS transcoding support

- Introduced `TranscodeManager` for managing on-demand transcoding of local video files.
- Added configuration options for transcoding in `Config` and `LocalFilesConfig`.
- Implemented new API routes for managing transcoding settings, stats, and cache.
- Updated `LocalFilesProvider` to support transcoding capabilities.
- Created frontend components for managing transcode settings and displaying stats.
- Added database migration for transcode settings.
- Enhanced existing routes and DTOs to accommodate new transcoding features.

k-tv-backend/api/src/dto.rs

@@ -235,6 +235,26 @@ pub struct ScheduleResponse {
     pub slots: Vec<ScheduledSlotResponse>,
 }
 
+// ============================================================================
+// Transcode DTOs
+// ============================================================================
+
+#[derive(Debug, Serialize)]
+pub struct TranscodeSettingsResponse {
+    pub cleanup_ttl_hours: u32,
+}
+
+#[derive(Debug, Deserialize)]
+pub struct UpdateTranscodeSettingsRequest {
+    pub cleanup_ttl_hours: u32,
+}
+
+#[derive(Debug, Serialize)]
+pub struct TranscodeStatsResponse {
+    pub cache_size_bytes: u64,
+    pub item_count: usize,
+}
+
 impl From<domain::GeneratedSchedule> for ScheduleResponse {
     fn from(s: domain::GeneratedSchedule) -> Self {
         Self {