fix(genapi): scope method-param enums per method, dedupe case-colliding enum consts

Bot API update added RichBlockListItem.type values (a/A/i/I/1) that
Pascal-case to identical const idents, and answerGuestQuery's non-enum
'result' param picked up answerChatJoinRequestQuery's Result enum via
the shared parent="" enum-plan key.

- key method params as method:<name> in the enum plan byField map
- enumDecl.ConstName resolves case collisions with Lower/Upper prefix
- regenerate api/ from 2026-06-11 snapshot

cmd/genapi/enums.tmpl

@@ -8,6 +8,6 @@ package api
 type {{$e.Name}} string
 
 const (
-{{range $v := $e.Values}}	{{enumConstName $e.Name $v}} {{$e.Name}} = {{printf "%q" $v}}
+{{range $v := $e.Values}}	{{$e.ConstName $v}} {{$e.Name}} = {{printf "%q" $v}}
 {{end}})
 {{end}}