Convert post edit form from raw HTML to SX expressions

Replace _post_edit_content_sx raw HTML builder with sx_call() pattern
matching render_editor_panel. Add ~blog-editor-edit-form,
~blog-editor-publish-js, ~blog-editor-sx-initial components to
editor.sx. Fixes (~sx-editor-styles) rendering as literal text on
the edit page.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/sx/helpers.py

@@ -378,6 +378,7 @@ def sx_call(component_name: str, **kwargs: Any) -> str:
     return "(" + " ".join(parts) + ")"
 
 
+
 def components_for_request() -> str:
     """Return defcomp/defmacro source for definitions the client doesn't have yet.