fix: suppress Rust dead code warnings with annotations

- ExportEvent::Error and DownloadEvent::Error reserved for future use
- clip_exporter functions scaffolded for caption burn-in pipeline
- SubtitleFormat fields required for serde deserialization

Co-authored-by: Cursor <cursoragent@cursor.com>

src-tauri/src/services/video_resolver.rs

@@ -4,6 +4,7 @@ use std::collections::HashMap;
 use std::process::Command;
 
 #[derive(Debug, Deserialize)]
+#[allow(dead_code)] // Fields used for serde deserialization
 pub struct SubtitleFormat {
     pub ext: Option<String>,
     pub url: Option<String>,