perf(desktop): reduce CPU/GPU overhead in Tauri shell

- SSH monitor: adaptive polling 2s→10s after stabilization, cheap TCP
  probe before expensive SSH subprocess check
- SSH setup: exponential backoff in wait_for_master_ready and
  wait_local_forward_ready (250ms→2s cap)
- Health checks: exponential backoff (100ms→1s / 250ms→2s) instead of
  flat intervals
- Startup recovery poll: cap at 15 retries instead of infinite
- Remove webview log target in release builds (eliminates IPC overhead)
- Set global NO_PROXY env var at startup for all loopback addresses
- Remove reqwest::blocking feature; use raw TCP for sidecar shutdown and
  SSH health checks
- Disable pinch-to-zoom on macOS via WKWebView.setAllowsMagnification
- Add WebView2 browser args on Windows (proxy bypass + disable unused
  UI features)
- Add Cargo release profile: thin LTO, codegen-units=1, strip
- Extract apply_platform_window_config for consistent window setup
- Add vibrancy toggle in Appearance settings (macOS desktop only) with
  solid background fallback when disabled

packages/ui/src/styles/design-system.css

@@ -135,12 +135,29 @@
     overscroll-behavior-y: none;
   }
 
-  :root.desktop-runtime body,
-  :root.desktop-runtime #root {
+  :root.desktop-runtime:not(.no-vibrancy) body,
+  :root.desktop-runtime:not(.no-vibrancy) #root {
     background: transparent !important;
     background-color: transparent !important;
   }
 
+  :root.desktop-runtime.no-vibrancy body,
+  :root.desktop-runtime.no-vibrancy #root {
+    background: var(--background) !important;
+    background-color: var(--background) !important;
+  }
+
+  /* When vibrancy is off, force sidebar overlays to solid and disable blur. */
+  :root.desktop-runtime.no-vibrancy {
+    --sidebar-overlay-strong: var(--sidebar) !important;
+    --sidebar-overlay-soft: var(--sidebar) !important;
+  }
+
+  :root.desktop-runtime.no-vibrancy .backdrop-blur {
+    -webkit-backdrop-filter: none !important;
+    backdrop-filter: none !important;
+  }
+
   .font-sans {
     font-family: var(--font-sans, -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif) !important;
   }