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

Dockerfile

@@ -1,6 +1,6 @@
 # syntax=docker/dockerfile:1.7
 #
-# ScopeNet admin panel — a single static binary + the web UI on `scratch`.
+# SCOPENET admin panel — a single static binary + the web UI on `scratch`.
 # Multi-arch (amd64/arm64) is cross-compiled with cargo-zigbuild on the
 # build machine's native arch, so no slow QEMU emulation is needed.
 
@@ -29,7 +29,7 @@ WORKDIR /src
 COPY . .
 # No --locked: release builds stamp the version into Cargo.toml. Dependencies
 # stay pinned by Cargo.lock either way (CI enforces --locked).
-RUN --mount=type=cache,target=/usr/local/cargo/registry,id=cargo-registry \
+RUN --mount=type=cache,target=/usr/local/cargo/registry,id=cargo-registry,sharing=locked \
     --mount=type=cache,target=/src/target,id=scopenet-target-$TARGETARCH \
     cargo zigbuild --release -p scopenet-panel --target "$(cat /rust-target)" \
  && cp "target/$(cat /rust-target)/release/scopenet-panel" /scopenet-panel
@@ -38,8 +38,8 @@ RUN mkdir -p /out/data && chown 65532:65532 /out/data
 
 # ---- 3. Runtime --------------------------------------------------------------
 FROM scratch
-LABEL org.opencontainers.image.title="ScopeNet Panel" \
-      org.opencontainers.image.description="Admin panel for the ScopeNet Minecraft launcher" \
+LABEL org.opencontainers.image.title="SCOPENET Panel" \
+      org.opencontainers.image.description="Admin panel for the SCOPENET Minecraft launcher" \
       org.opencontainers.image.source="https://github.com/scopeddlol/SCOPENET-MC"
 COPY --from=build /scopenet-panel /scopenet-panel
 COPY --from=web /src/panel/web/dist /web