fix(compiler): never emit an empty pattern attribute

An empty pattern compiles to a regex matching only the empty string, so
every typed value becomes invalid and the form silently refuses to submit
-- no error, no request. @wrnexus/ui's input declares pattern: string = ""
and renders pattern="{pattern}", so every input that did not opt into a
pattern shipped one that could never match. This broke sign-up in a real
app, and only became visible once the dev-server client-module fix let
form enhancements mount at all.

Attributes reach the output through two emitters and both needed it: a
component's interpolated value is baked at render time, so the whole
attribute is now emitted by __wrnOptionalAttr, while a page's static
element is dropped at compile time. Component mounts are excluded, where
the value is a prop being passed down rather than an attribute.

minlength/maxlength/min/max/step/inputmode/accept get the same treatment --
inert when empty, but meaningless too.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/compiler/test/__snapshots__/resilience.test.ts.snap

@@ -133,6 +133,10 @@ function __wrnHtml(v: unknown): string {
   );
 }
 
+function __wrnOptionalAttr(name: string, value: string): string {
+  return value === "" ? "" : " " + name + '="' + value + '"';
+}
+
 function __wrnAttr(v: unknown): string {
   return String(v == null ? "" : v).replace(
     /[&<>"]/g,