Restore mac traffic lights without enabling native chrome on Linux/Windows

Keep custom chrome on non-mac platforms while restoring native traffic lights on macOS. Also remove the extra outer mac shell radius/border to avoid double-rounded corners.

Constraint: macOS must show native traffic lights for issue #183
Constraint: Windows/Linux should keep custom titlebar behavior
Rejected: set decorations=true in tauri.conf globally | enables native chrome on Linux
Confidence: high
Scope-risk: narrow
Directive: Platform-specific window decoration behavior should be controlled at runtime, not by global config
Tested: npm run build (openless-all/app)
Not-tested: manual visual verification on real macOS/Linux/Windows runtimes

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

@@ -93,6 +93,9 @@ pub fn run() {
                     use window_vibrancy::{
                         apply_vibrancy, NSVisualEffectMaterial, NSVisualEffectState,
                     };
+                    if let Err(e) = main.set_decorations(true) {
+                        log::warn!("[main] enable native decorations failed: {e}");
+                    }
                     if let Err(e) = apply_vibrancy(
                         &main,
                         NSVisualEffectMaterial::HudWindow,

openless-all/app/src/components/WindowChrome.tsx

@@ -47,7 +47,7 @@ export function WindowChrome({
   children,
   height = 800,
 }: WindowChromeProps) {
-  const shellRadius = os === 'mac' ? 20 : os === 'win' ? WIN_WINDOW_RADIUS : 14;
+  const shellRadius = os === 'mac' ? 0 : os === 'win' ? WIN_WINDOW_RADIUS : 14;
   const consoleRadius = os === 'mac' ? 20 : os === 'win' ? WIN_CONSOLE_RADIUS : 14;
 
   return (
@@ -66,7 +66,11 @@ export function WindowChrome({
         overflow: 'hidden',
         display: 'flex',
         flexDirection: 'column',
-        border: os === 'win' ? '1px solid rgba(255,255,255,0.18)' : '0.5px solid rgba(0,0,0,.10)',
+        border: os === 'mac'
+          ? 'none'
+          : os === 'win'
+            ? '1px solid rgba(255,255,255,0.18)'
+            : '0.5px solid rgba(0,0,0,.10)',
         background: `
           radial-gradient(120% 80% at 0% 0%, rgba(255,255,255,0.7) 0%, rgba(255,255,255,0) 60%),
           radial-gradient(100% 70% at 100% 100%, rgba(37,99,235,0.07) 0%, rgba(37,99,235,0) 55%),