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/audio/src/capture.rs

@@ -112,7 +112,7 @@ impl MicrophoneCapture {
         for device in devices {
             let name = device_display_name(&device).unwrap_or_else(|| "<unnamed>".to_string());
             let (sample_rate, channels) = match device.default_input_config() {
-                Ok(cfg) => (cfg.sample_rate(), cfg.channels() as u16),
+                Ok(cfg) => (cfg.sample_rate(), cfg.channels()),
                 Err(_) => (0, 0),
             };
             let is_likely_monitor = is_monitor_name(&name);
@@ -278,7 +278,7 @@ fn device_display_name(device: &cpal::Device) -> Option<String> {
 fn extract_card_id(name: &str) -> Option<&str> {
     let rest = name.split("CARD=").nth(1)?;
     Some(
-        rest.split(|c: char| c == ',' || c == ';')
+        rest.split([',', ';'])
             .next()
             .unwrap_or(rest),
     )
@@ -361,7 +361,7 @@ fn open_and_validate(
         .default_input_config()
         .map_err(|e| KonError::AudioCaptureFailed(format!("default_input_config: {e}")))?;
     let sample_rate = config.sample_rate();
-    let channels = config.channels() as u16;
+    let channels = config.channels();
     let format = config.sample_format();
 
     eprintln!(