chore(lint): clean up clippy warnings across workspace

Auto-applied cargo clippy --fix across 11 files — needless return,
unnecessary cast, map_or simplification, repeat().take() → repeat_n(),
iter().any() → contains(), manual char comparison, lifetime elision,
push_str single-char, reference immediately dereferenced.

Also fixed three lints on file_storage.rs manually: two doc-list-item
overindentations, plus the same needless-return. Baseline main was
not clippy-clean with -D warnings before; after this pass one
needless_range_loop warning remains (live.rs:1089) that clippy's
suggested rewrite would make less readable — left for a dedicated
refactor session.

Build + workspace tests remain green (245 passing, 0 failing, 1
ignored).

crates/transcription/src/streaming/buffer_trim.rs

@@ -158,7 +158,7 @@ mod tests {
         let mut total_pushed: u64 = 0;
         let tentative_per_cycle: u64 = 200;
         for _ in 0..100 {
-            buf.extend(std::iter::repeat(0.25_f32).take(16_000));
+            buf.extend(std::iter::repeat_n(0.25_f32, 16_000));
             total_pushed += 16_000;
             let commit_point = total_pushed - tentative_per_cycle;
             start = trim_buffer_to_commit_point(&mut buf, start, commit_point);
@@ -199,7 +199,7 @@ mod tests {
 
         // Simulate a capture buffer that has received 1.2 s of audio
         // starting at t=0.
-        let mut buf: Vec<f32> = std::iter::repeat(0.1_f32).take(19_200).collect();
+        let mut buf: Vec<f32> = std::iter::repeat_n(0.1_f32, 19_200).collect();
         let new_start = trim_buffer_to_commit_point(&mut buf, 0, commit_idx);
         assert_eq!(new_start, 8_000);
         assert_eq!(buf.len(), 19_200 - 8_000);