Published Docker image serves fallback dashboard

Summary
The published Docker image biancarosa/netkit:0.1.0 serves the fallback dashboard page when started with serve --dashboard. The binary help output also lacks dashboard-base-path, so runtime NETKIT_DASHBOARD_BASE_PATH is not available for path-prefix reverse proxy deployments.

Repro
1. Run biancarosa/netkit:0.1.0 with serve --dashboard --dashboard-port 3000 --admin-port 8081.
2. Open the dashboard port in a browser.
3. The page says Dashboard not embedded and explains that the build does not include the embedded dashboard.

Expected
The published image should serve the real dashboard, or docs/release notes should clearly state that a separate dashboard-dir is required. The image should support dashboard-base-path / NETKIT_DASHBOARD_BASE_PATH for path-prefix deployments once that feature is released.

Notes
A newer development branch appears to add base-path support and Dockerfile validation for the embedded dashboard, so this may be a release/image publishing issue rather than an application runtime bug.

Start by inspecting how the published biancarosa/netkit:0.1.0 image is built and whether the embedded dashboard is included, then compare it with the newer development branch's Dockerfile validation and dashboard-base-path support. Reproduce the serve --dashboard command and check the binary help output. Done means the image serves the real dashboard or clearly documents the separate dashboard-dir requirement, with dashboard-base-path support available when released.

Written by the indexing model from the issue text.