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/src/commands.rs

@@ -79,7 +79,7 @@ async fn fetch_manifest(state: &AppState, panel: &str) -> anyhow::Result<Launche
     if !resp.status().is_success() {
         anyhow::bail!("{panel} returned {}", resp.status());
     }
-    let m: LauncherManifest = resp.json().await.map_err(|_| anyhow::anyhow!("{panel} doesn't look like a ScopeNet panel"))?;
+    let m: LauncherManifest = resp.json().await.map_err(|_| anyhow::anyhow!("{panel} doesn't look like a SCOPENET panel"))?;
     Ok(m)
 }