feat: make schema hash in header comment opt-in via -schemaHash

The schema hash in the OpenAPI header comment changes on every schema edit,
producing perpetual git merge conflicts in the generated YAML.

Gate the hash behind a new -schemaHash target option (default false), flipping
the previous always-on behavior:

- default: header comment carries only the name and version (no hash). The
  "Code generated by ... DO NOT EDIT." line stays.
- with -schemaHash: restores today's output exactly (hash in the header).

This generator emits only a header comment (no version helper functions or
constants exist here), so the gate is comment-only. Mirrors the sibling
gen-golang change.

Regenerated _examples to reflect the new default.

Author: klaidliadon

_examples/openapi.gen.yaml

@@ -1,4 +1,4 @@
-# example v1.0.0 ceb35c0c54325918ffdd24bf625bb6c8c941f75e
+# example v1.0.0
 # --
 # Code generated by webrpc-gen@v0.37.0 with ../ generator; DO NOT EDIT
 # 

main.go.tmpl

@@ -9,6 +9,7 @@
 {{- set $opts "servers" (default .Opts.servers "") -}}
 {{- set $opts "securityAnnotation" (default .Opts.securityAnnotation "") -}}
 {{- set $opts "securitySchemes" (default .Opts.securitySchemes "") -}}
+{{- set $opts "schemaHash" (ternary (in .Opts.schemaHash "" "true") true false) -}}
 
 {{- /* Print help on -help. */ -}}
 {{- if exists .Opts "help" -}}
@@ -65,7 +66,7 @@
 {{- $webrpcErrors := .WebrpcErrors -}}
 {{- $schemaErrors := .Errors -}}
 
-# {{.SchemaName}} {{.SchemaVersion}} {{.SchemaHash}}
+# {{.SchemaName}} {{.SchemaVersion}}{{if $opts.schemaHash}} {{.SchemaHash}}{{end}}
 # --
 # Code generated by webrpc-gen@{{.WebrpcGenVersion}} with {{.WebrpcTarget}} generator; DO NOT EDIT
 #