chore: cargo clippy --fix 自动清理小手术 (closes #170)

cargo clippy --fix 自动修了 8 个 lint，warnings 从 18 降到 16。

改动文件：
- asr/mod.rs / coordinator.rs / hotkey.rs / insertion.rs / polish.rs / types.rs
- 主要是 needless_borrow / single_match / useless_conversion / 多余 cast

build 跑过：
- cargo check ✅
- npm run build ✅

剩余 16 个 warning 都是有意保留的（test-only helpers、future-API placeholder、
类似 TodayMetrics 这种历史接口），不动这些避免破坏 surface。issue #170
里更深层的整洁度（SettingsWriter dedupe / force 参数删除等）后续 PR 跟进。

openless-all/app/src-tauri/src/asr/mod.rs

@@ -9,7 +9,7 @@ mod frame;
 pub mod volcengine;
 pub mod whisper;
 
-pub use volcengine::{VolcengineASRError, VolcengineCredentials, VolcengineStreamingASR};
+pub use volcengine::{VolcengineCredentials, VolcengineStreamingASR};
 pub use whisper::WhisperBatchASR;
 
 /// Sink for raw 16 kHz / 16-bit / mono PCM bytes coming off the recorder.

openless-all/app/src-tauri/src/coordinator.rs

@@ -749,7 +749,7 @@ async fn handle_window_hotkey_event(
     #[cfg(not(target_os = "windows"))]
     {
         let _ = (inner, event_type, key, code, repeat);
-        return Ok(());
+        Ok(())
     }
 
     #[cfg(target_os = "windows")]
@@ -2599,7 +2599,6 @@ fn maybe_position_capsule_bottom_center<R: tauri::Runtime>(
     if crate::position_capsule_bottom_center(window, translation_active).is_ok() {
         let mut last = inner.capsule_layout.lock();
         *last = Some(next);
-        return;
     }
 }
 

openless-all/app/src-tauri/src/hotkey.rs

@@ -164,7 +164,7 @@ mod platform {
             "hotkey hook 启动超时",
             run_listen_loop,
         )?;
-        let _ = listener.startup;
+        listener.startup;
         Ok(Box::new(MacHotkeyAdapter {
             shared: listener.shared,
         }))

openless-all/app/src-tauri/src/insertion.rs

@@ -10,7 +10,6 @@
 //!    → CGEventPost，跟我们这里完全同源。
 //! 3. 其他平台 (Windows/Linux) 仍用 enigo。
 
-use std::time::Duration;
 
 use crate::types::InsertStatus;
 

openless-all/app/src-tauri/src/polish.rs

@@ -606,10 +606,9 @@ const BOILERPLATE_END_CHARS: &[char] = &['。', '：', ':', '，', ',', '\n'];
 
 fn strip_leading_boilerplate(text: &str) -> &str {
     for prefix in LEADING_BOILERPLATE_PREFIXES {
-        if text.starts_with(prefix) {
+        if let Some(after_prefix) = text.strip_prefix(prefix) {
             // Trim characters after the prefix up to (and including) the first
             // sentence-ending punctuation or newline.
-            let after_prefix = &text[prefix.len()..];
             for (idx, c) in after_prefix.char_indices() {
                 if BOILERPLATE_END_CHARS.contains(&c) {
                     let cut = prefix.len() + idx + c.len_utf8();

openless-all/app/src-tauri/src/types.rs

@@ -4,18 +4,15 @@ use serde::{Deserialize, Serialize};
 
 #[derive(Debug, Clone, Copy, Serialize, Deserialize, PartialEq, Eq)]
 #[serde(rename_all = "lowercase")]
+#[derive(Default)]
 pub enum PolishMode {
     Raw,
+    #[default]
     Light,
     Structured,
     Formal,
 }
 
-impl Default for PolishMode {
-    fn default() -> Self {
-        PolishMode::Light
-    }
-}
 
 impl PolishMode {
     pub fn display_name(&self) -> &'static str {
@@ -300,7 +297,7 @@ impl HotkeyCapability {
     pub fn current() -> Self {
         #[cfg(target_os = "macos")]
         {
-            return Self {
+            Self {
                 adapter: HotkeyAdapterKind::MacEventTap,
                 available_triggers: vec![
                     HotkeyTrigger::RightOption,
@@ -315,7 +312,7 @@ impl HotkeyCapability {
                 supports_side_specific_modifiers: true,
                 explicit_fallback_available: false,
                 status_hint: Some("授权辅助功能后，通常需要完全退出并重新打开 OpenLess。".into()),
-            };
+            }
         }
 
         #[cfg(target_os = "windows")]