chore: cargo fmt + clippy fix for collapsed if-let chain (T017)

- cargo fmt applied across all modified source files
- Collapse nested if let Some / if !is_empty into a single let-chain (clippy::collapsible_match)
- All other warnings are pre-existing dead-code lint on unused trait methods

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/video/ffmpeg.rs

@@ -183,7 +183,11 @@ impl Ffmpeg {
         Ok(output_file.to_string())
     }
 
-    pub async fn create_gif_from_frames(&self, frame_base_dir: &str, output_file: &str) -> Result<i32> {
+    pub async fn create_gif_from_frames(
+        &self,
+        frame_base_dir: &str,
+        output_file: &str,
+    ) -> Result<i32> {
         let output = Command::new("ffmpeg")
             .arg("-y")
             .args(["-framerate", "4"])
@@ -278,10 +282,7 @@ pub async fn generate_preview_clip(input_file: &str, output_file: &str) -> Resul
             "select='lt(mod(t,{:.4}),1)',setpts=N/FRAME_RATE/TB,fps=30,scale=-2:480,format=yuv420p",
             interval
         );
-        let af = format!(
-            "aselect='lt(mod(t,{:.4}),1)',asetpts=N/SR/TB",
-            interval
-        );
+        let af = format!("aselect='lt(mod(t,{:.4}),1)',asetpts=N/SR/TB", interval);
 
         cmd.args(["-vf", &vf]);
         cmd.args(["-af", &af]);
@@ -326,7 +327,10 @@ pub async fn generate_preview_clip(input_file: &str, output_file: &str) -> Resul
 
     info!(
         "Generated preview clip '{}' ({:.1}s, {} bytes) in {:?}",
-        output_file, clip_duration, file_size, start.elapsed()
+        output_file,
+        clip_duration,
+        file_size,
+        start.elapsed()
     );
 
     Ok((clip_duration, file_size))