Asynchronous JavaScript execution

[noise64]

• resolves GOL-54
• adds asynchronous inline and entry-module execution with concurrent isolated QuickJS runtimes
• keeps mutable process, timer, filesystem, descriptor, module, and JavaScript state fresh per job while sharing component capabilities and filesystem
• exposes live stdout/stderr, bounded capture, structured results, cancellation, capacity limits, and absolute wall-clock timeouts
• supports cwd-relative ESM, CommonJS, JSON, and package resolution on Preview 2 and Preview 3
• adds focused runtime coverage for concurrency, isolation, imports, output lifecycle, timeout, overflow, cancellation, structured-clone edge cases, and capacity reclamation
• documents that this is context isolation rather than a security sandbox