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).

src-tauri/src/commands/paste.rs

@@ -345,7 +345,7 @@ fn classify_terminal(raw: &str) -> Option<String> {
 fn detect_focused_window_class() -> Option<String> {
     #[cfg(target_os = "linux")]
     {
-        return detect_focused_window_class_linux();
+        detect_focused_window_class_linux()
     }
     #[cfg(target_os = "macos")]
     {