fix: prevent owned VM fetch wakeup starvation

[NathanFlurry]

• Make the ordinary dispatcher the sole owner of guest execution events while owned VM fetches wake it during async progress.
• Propagate loopback hangups through JavaScript HTTP cleanup so stream cancellation releases peer resources.
• Add repeated WebSocket-dependent streaming coverage and the Node HTTP/2 exports required by the Dynamic Apps reproducer.
• Validate with focused Rust/TypeScript tests and the Dynamic Apps health, metadata, direct HTTP, and SQLite sanity flow.

[railway-app]

🚅 Environment agentos-pr-1937 in rivet-frontend has no services deployed.