Ruby/Rails server v2 (framework-agnostic adapter)

[bradgessler]

Reimplement the server against the v2 protocol.

• Minimal framework-agnostic server adapter (read/write/close over a connection); Rails/ActionCable becomes one impl behind it, plus a plain Rack/Falcon reference.
• Drop the v1 back-compat module Thor shim and the rigid authority→policy resolution.
• Keep the Thor ask_simply stdin/stdout redirection magic.
• Validated against the conformance harness as a server impl.