Add baseline Lua workers on C11 threads with copy-based channels

[Copilot]

• Inspect the current worker implementation, Lua wrapper, and focused tests
• Rebuild the focused worker harness and run current worker tests as a baseline
• Update the Lua worker API to accept functions or file paths as jobs, with a single context argument
• Add one-shot wait/run helpers and waiting support for multiple tasks
• Expand focused worker tests for function jobs, file jobs, single-task wait, and multi-task wait
• Re-run the focused worker compile/test validation and address any issues
• Run final review/security validation and summarize any remaining limitations