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

.github/workflows/release.yml

@@ -6,7 +6,7 @@ name: Release
 # Optional repository variables (Settings → Secrets and variables → Actions → Variables):
 #   PANEL_URL      https://panel.example.com — baked into the launcher as the default server
 #   LOCK_PANEL     "1" to stop players from changing the server
-#   LAUNCHER_NAME  Installer / window name (default "ScopeNet Launcher")
+#   LAUNCHER_NAME  Installer / window name (default "SCOPENET Launcher")
 
 on:
   push: