Speech runtime was leaking 8+ individual resolvers into bootstrap and
blocking server startup for ~3s with synchronous Sherpa native model
loading. Refactor into a self-contained SpeechService that owns its
full lifecycle (init, download, monitor, cleanup) and defer start()
until after httpServer.listen() so native loading doesn't block
accepting connections. Server startup drops from ~3.2s to ~0.5s.
Also removes unused client-triggered speech model download/list path
(CLI commands, session handlers, message types) — the service manages
its own models.