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/tauri.conf.json

@@ -1,6 +1,6 @@
 {
   "$schema": "https://schema.tauri.app/config/2",
-  "productName": "ScopeNet Launcher",
+  "productName": "SCOPENET Launcher",
   "version": "0.1.0",
   "identifier": "net.scopenet.launcher",
   "build": {
@@ -14,7 +14,7 @@
     "windows": [
       {
         "label": "main",
-        "title": "ScopeNet Launcher",
+        "title": "SCOPENET Launcher",
         "width": 1120,
         "height": 700,
         "minWidth": 960,
@@ -33,7 +33,7 @@
   "bundle": {
     "active": true,
     "targets": ["nsis"],
-    "publisher": "ScopeNet",
+    "publisher": "SCOPENET",
     "category": "Game",
     "shortDescription": "Minecraft launcher",
     "longDescription": "A fast, customisable Minecraft launcher connected to your community's admin panel.",