feat(mini-player): custom titlebar with action icons; cover/meta/controls layout polish

- Drop the native titlebar on Windows + Linux (decorations: false in
  open_mini_player); macOS keeps the system titlebar with traffic lights.
- Add a slim 26 px custom titlebar with drag region, current track
  title, and the queue / pin / open-main / close action icons.
- Remove the bottom toolbar — those four buttons now live in the
  titlebar where they're easier to reach.
- Refresh the player layout: cover shrinks 112 → 84 px, the right
  column gets title / artist / transport in a single 84 px-tall block,
  progress bar spans the full width below.
- Add a miniPlayer i18n namespace (showQueue, hideQueue, pinOnTop,
  pinOff, openMainWindow, close, emptyQueue) localized for all 8
  supported locales — previously the tooltips were hard-coded English.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src-tauri/src/lib.rs

@@ -2756,6 +2756,11 @@ fn open_mini_player(app: tauri::AppHandle) -> Result<(), String> {
         .map(|m| m.scale_factor())
         .unwrap_or(1.0);
 
+    // macOS keeps the native titlebar (traffic lights + system look).
+    // Windows and Linux use a custom in-page titlebar so the mini fits a
+    // tighter visual style across all WMs (incl. tiling).
+    let use_decorations = cfg!(target_os = "macos");
+
     let mut builder = tauri::WebviewWindowBuilder::new(
         &app,
         "mini",
@@ -2765,7 +2770,7 @@ fn open_mini_player(app: tauri::AppHandle) -> Result<(), String> {
     .inner_size(340.0, 180.0)
     .min_inner_size(320.0, 180.0)
     .resizable(true)
-    .decorations(true)
+    .decorations(use_decorations)
     .always_on_top(use_always_on_top)
     .skip_taskbar(false);