feat(build): make generated page helper canonical

Move canonical examples and docs snippets from raw render/page calls to generated ui::page helpers, hide generated render behind doc(hidden), and let form resources participate in generated target inspection for tests.

req: canonical_authoring/005

req: dx/006

req: codegen/002

req: public_api/002

req: test/001

hemx-core/src/lib.rs

@@ -1165,6 +1165,12 @@ impl<T> core::fmt::Display for Form<T> {
     }
 }
 
+impl<T> GeneratedTarget for Form<T> {
+    fn __hemx_resource_id(self) -> ResourceId {
+        self.id
+    }
+}
+
 impl<T> Form<T> {
     pub const fn new(id: u32) -> Self {
         Self {