Restyle to a clean, flat look and rename brand to SCOPENET

- Brand is now SCOPENET everywhere (defaults, UI, installer, docs)
- Launcher: solid backgrounds (no animated orbs/grain), flat Play button
  without gradient/shine/glow, quieter rail with a simple active
  indicator, smaller type scale, Inter as default font, glass off by
  default, restyled sliders
- Panel: same flat treatment; live preview mirrors the new launcher
- New flat scope-reticle logo and app icons
- Calmer default palette
- Fix: lock the shared cargo cache in the Docker build (amd64/arm64 raced)
- Fix: Windows-only clippy lint in sys.rs

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011ARcGWxLx21FwXJ3yfGriS

panel/web/src/components/Toasts.svelte

@@ -17,7 +17,7 @@
   .toasts { position: fixed; right: 20px; bottom: 20px; display: flex; flex-direction: column; gap: 10px; z-index: 100; max-width: 420px; }
   .toast {
     display: flex; align-items: center; gap: 10px; padding: 10px 10px 10px 14px; border-radius: 12px;
-    background: rgba(24, 27, 41, 0.92); backdrop-filter: blur(12px); border: 1px solid var(--line-strong);
+    background: var(--surface-2); border: 1px solid var(--line-strong);
     box-shadow: var(--shadow); animation: pop 0.2s ease; font-size: 0.9rem;
   }
   .toast span { flex: 1; }