test(techdemo): exercise checked form handler path

Add techdemo coverage for #[slhx::form] plus #[slhx::handler] on the generated launch_work form, and ignore the internal __h hidden handle field in generated form metadata.

req: form/001

req: form/004

req: form/006

req: derive_handler/003

slhx-build/src/lib.rs

@@ -276,6 +276,10 @@ impl Resources {
         component: String,
         controls: Vec<GeneratedControl>,
     ) -> io::Result<()> {
+        let controls = controls
+            .into_iter()
+            .filter(|control| control.name != "__h")
+            .collect();
         let resource = make_resource("form", symbol, name, component, false)?;
         match self.forms.get(&resource.ident) {
             Some(existing) if existing.resource.symbol != resource.symbol => Err(io::Error::new(
@@ -1062,6 +1066,7 @@ mod tests {
         std::fs::write(
             templates.join("profile.heml"),
             r#"<form data-slhx-handle="save" data-slhx-form="profile">
+                <input type="hidden" name="__h" value="123">
                 <input name="title" required>
                 <input name="count" type="number" min="1" max="10" step="1">
                 <select name="labels" multiple></select>
@@ -1090,6 +1095,7 @@ mod tests {
 
         let syms = std::fs::read_to_string(out.join("slhx.syms")).unwrap();
         assert!(syms.contains("handle_form\tsave\tprofile\n"));
+        assert!(!syms.contains("form_field\tprofile\t__h\t"));
         assert!(syms.contains("form_field\tprofile\ttitle\ttrue\tfalse\n"));
         assert!(syms.contains("form_field\tprofile\tlabels\tfalse\ttrue\n"));