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/rms_vad.rs

@@ -306,7 +306,7 @@ impl VadChunker for RmsVadChunker {
                 .saturating_sub(self.pending.len() as u64);
             let pad_len = FRAME_SAMPLES - self.pending.len();
             let mut padded = std::mem::take(&mut self.pending);
-            padded.extend(std::iter::repeat(0.0_f32).take(pad_len));
+            padded.extend(std::iter::repeat_n(0.0_f32, pad_len));
             if let Some(chunk) = self.consume_frame(padded, frame_start) {
                 emitted.push(chunk);
             }