- Change @anthropic-ai/sdk-inspector to @sandbox-agent/inspector in all Dockerfiles
- Add .dockerignore to exclude target/, node_modules/, etc from Docker context
The wrong package name caused pnpm install --filter to match nothing, so the
inspector frontend was never built, resulting in binaries without the /ui/ endpoint.
## Summary
- Add Node.js build stage to all release Dockerfiles to build the inspector frontend
- Copy pre-built inspector assets into Rust build stages so they get embedded in binaries
- Remove `SANDBOX_AGENT_SKIP_INSPECTOR=1` from all Dockerfiles and the release workflow
## Test plan
- [ ] Build linux-x86_64 locally: `docker/release/build.sh x86_64-unknown-linux-musl`
- [ ] Run the binary and verify inspector is embedded (should show "inspector ui available")
- [ ] Access the inspector UI at http://localhost:2468/ui/🤖 Generated with [Claude Code](https://claude.ai/code)
