feat(api): streamline generated app authoring

Move the canonical examples toward generated component-root helpers, typed form decoding, async/state handler registration, and derive-driven app/component registry wiring. Tighten requirements and diagnostics for the server-first, selectorless authoring path.

Verified with cargo run -p slhx-xtask -- test, cargo check --workspace, redgate list, redgate refs, redgate health --strict, and git diff --check.

req: canonical/001

req: canonical/003

req: canonical/004

req: dx/002

req: derive_app/001

req: component/003

req: form/004

req: axum_integration/003

examples/v0/templates/todos.heml

@@ -3,9 +3,21 @@
     <input name="title" required="required">
     <button type="submit">Add</button>
   </form>
-  <ul data-slhx-slot="todo_list">
-    <template h-for="todo in &self.todos" h-key="todo.id">
-      <li data-slhx-slot="todo_row">{+ todo.title +}</li>
-    </template>
-  </ul>
+  <p data-slhx-slot="summary">{+ self.summary +}</p>
+  <div data-slhx-slot="todo_list">
+    <ul data-slhx-slot="todo_row">
+      <template h-for="todo in &self.items" h-key="todo.id">
+        <li data-slhx-slot="todo_row" +data-key="todo.id">
+          <span>{+ todo.title +}</span>
+          <form data-slhx-handle="rename_todo">
+            <input type="hidden" name="id" +value="todo.id">
+            <button type="submit" name="title" value="Renamed todo">Rename</button>
+          </form>
+          <form data-slhx-handle="delete_todo">
+            <button type="submit" name="id" +value="todo.id">Delete</button>
+          </form>
+        </li>
+      </template>
+    </ul>
+  </div>
 </section>