Improves error handling for canceled requests

Update internal/api/modules/amp/proxy.go

Update internal/api/modules/amp/proxy.go

feature(proxy): Adds special handling for client cancellations in proxy error handler

feat(amp): add per-client upstream API key mapping support

feat(amp): require API key authentication for management routes

style(amp): tidy whitespace in proxy module and tests

fix(amp): filter context-1m beta header for local OAuth providers

feat: Add Amp CLI integration with comprehensive documentation