Introduce cmd/lint to statically verify operator templates vs routes
(internal/lint). Replace interpolated hx-* URL strings with operatorURL
calls in partials, register operatorURL in the template FuncMap,
add server/operator_url.go with unit tests, and update go.mod.
Add routeURL helper and template linter
Introduce web.FieldErrors for server-side per-field messages. Update
templates to render is-invalid/invalid-feedback and add a fieldErr
template helper that scopes errors to a specific form instance. Update
operator handlers to validate inputs, populate FieldErrors, and render
form-specific error state; add a no-op fieldErr stub to fedwiki partials
so parsing succeeds.