Simplify JavaScript provider flow

[Nisheet Jain (nisheetjain)]

Summary

• make the Azure Function own the explicit parse, decrypt, evaluation/provider, credential, send, and response flow
• move provider protocol behavior and failure classification into the provider modules
• replace the dispatch registry and mutable request summary with focused JWE/transport/model modules and fixed structured events
• preserve credential caching, privacy controls, evaluation short-circuiting, and provider-specific SMS/voice behavior

Testing

• npm test (42 tests passed)