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/models.rs

@@ -412,7 +412,7 @@ pub fn detect_active_compute_device() -> ActiveComputeDevice {
                 reason: None,
             };
         }
-        return ActiveComputeDevice {
+        ActiveComputeDevice {
             kind: "cpu".into(),
             label: "CPU (fallback)".into(),
             reason: Some(
@@ -420,7 +420,7 @@ pub fn detect_active_compute_device() -> ActiveComputeDevice {
                  libvulkan1 (Linux) to enable GPU acceleration."
                     .into(),
             ),
-        };
+        }
     }
 }