Restyle admin UI to dark theme, fix Docker /data volume permissions

- Rework the admin UI (topbar, sidebar, cards, tables, badges, stat
  tiles) into a dark theme with a light/dark toggle, matching the
  visual style requested for the project.
- Fix Dockerfile: chown /data to the distroless nonroot uid/gid before
  the VOLUME declaration so a freshly created named volume is seeded
  with writable permissions instead of root:root (was causing
  "unable to open database file" on first run).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QTXFrNP1imCW7jtfL5SZrw

Dockerfile

@@ -5,9 +5,14 @@ RUN go mod download
 COPY . .
 ARG VERSION=dev
 RUN CGO_ENABLED=0 go build -trimpath -ldflags "-s -w -X main.Version=${VERSION}" -o /out/vibeproxy ./cmd/vibeproxy
+# distroless:nonroot runs as uid:gid 65532:65532 with no shell, so create
+# and own /data here — Docker seeds a fresh named volume's permissions
+# from the image directory it overlays, which is otherwise root:root.
+RUN mkdir -p /out/data && chown 65532:65532 /out/data
 
 FROM gcr.io/distroless/static-debian12:nonroot
 COPY --from=build /out/vibeproxy /usr/local/bin/vibeproxy
+COPY --from=build --chown=65532:65532 /out/data /data
 VOLUME ["/data"]
 # The nonroot container user can't bind ports <1024, so vibeproxy listens
 # on 8080/8443 inside the container; map host 80/443 to these in