feat(runtime): add online CPU source Dockerfile

[LauraGPT]

Summary

• add the missing source-build Dockerfile for the online CPU 2-pass WebSocket runtime
• rebuild the current checkout on the immutable public 0.1.13 multi-architecture toolchain image
• start funasr-wss-server-2pass directly with environment-variable model/thread/port overrides
• document source builds in English and Chinese and refresh the fallback image list through 0.1.13
• add a path-scoped GitHub Actions build plus linked-binary smoke test

Tracks #2807. Keep the issue open until the reporter confirms the source-built image works in their environment.

Validation

• 25 focused Docker/docs tests passed
• entrypoint bash syntax and override execution passed
• workflow YAML parsed successfully
• public 0.1.13 manifest verified for amd64 and arm64
• exact base digest and amd64 image config archived before push
• git diff --check passed
• signed SSH commit and DCO sign-off

The PR's online CPU Docker workflow performs the authoritative linux/amd64 image build and server --help smoke test on the exact head.