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

launcher/src-tauri/icons/logo.svg

@@ -1 +1 @@
-<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1024 1024"><defs><linearGradient id="g" x1="0" y1="0" x2="1" y2="1"><stop offset="0" stop-color="#8b6cff"/><stop offset="1" stop-color="#22d3ee"/></linearGradient><radialGradient id="glow" cx="0.5" cy="0.45" r="0.6"><stop offset="0" stop-color="#8b6cff" stop-opacity="0.35"/><stop offset="1" stop-color="#8b6cff" stop-opacity="0"/></radialGradient></defs><rect x="32" y="32" width="960" height="960" rx="224" fill="#0b0d17"/><rect x="32" y="32" width="960" height="960" rx="224" fill="url(#glow)"/><path d="M512 176 804 344v336L512 848 220 680V344z" fill="none" stroke="url(#g)" stroke-width="72" stroke-linejoin="round"/><path d="M512 176v168M804 344 660 428M220 344l144 84M512 848V680" stroke="url(#g)" stroke-width="40" stroke-linecap="round" opacity="0.45"/><circle cx="512" cy="512" r="112" fill="url(#g)"/></svg>
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1024 1024"><rect x="48" y="48" width="928" height="928" rx="208" fill="#16181e"/><circle cx="512" cy="512" r="236" fill="none" stroke="#ecedf1" stroke-width="64"/><circle cx="512" cy="512" r="72" fill="#6d6af5"/><path d="M512 196v120M512 708v120M196 512h120M708 512h120" stroke="#ecedf1" stroke-width="64" stroke-linecap="round"/></svg>