Replace sx_call() with render_to_sx() across all services

Python no longer generates s-expression strings. All SX rendering now
goes through render_to_sx() which builds AST from native Python values
and evaluates via async_eval_to_sx() — no SX string literals in Python.

- Add render_to_sx()/render_to_html() infrastructure in shared/sx/helpers.py
- Add (abort status msg) IO primitive in shared/sx/primitives_io.py
- Convert all 9 services: ~650 sx_call() invocations replaced
- Convert shared helpers (root_header_sx, full_page_sx, etc.) to async
- Fix likes service import bug (likes.models → models)

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

blog/bp/post/routes.py

@@ -125,7 +125,7 @@ def register():
 
       # Get post_id from g.post_data
       if not g.user:
-          return sx_response(render_like_toggle_button(slug, False, like_url), status=403)
+          return sx_response(await render_like_toggle_button(slug, False, like_url), status=403)
 
       post_id = g.post_data["post"]["id"]
       user_id = g.user.id
@@ -135,7 +135,7 @@ def register():
       })
       liked = result["liked"]
 
-      return sx_response(render_like_toggle_button(slug, liked, like_url))
+      return sx_response(await render_like_toggle_button(slug, liked, like_url))
 
   @bp.get("/w/<widget_domain>/")
   async def widget_paginate(slug: str, widget_domain: str):