echConfigList already accepted Xray's dynamic form, target domain + DoH URL,
but nothing in the inbound or host forms explained or built it. A helper now
builds that value from presets or a custom domain and resolver, accepts only the
schemes Xray dials (https, h2c, udp; scheme case normalised), warns that a key
generated locally does not work behind a CDN, and asks before overwriting local
ECH keys. The helper's controls carry accessible labels, and the resolver list
holds only identified public resolvers.