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>

shared/infrastructure/ap_social.py

@@ -92,14 +92,14 @@ def create_ap_social_blueprint(app_name: str) -> Blueprint:
         kw = {"actor": actor}
 
         if is_htmx_request():
-            oob_headers = _social_oob_headers(tctx, **kw)
-            return sx_response(oob_page_sx(
+            oob_headers = await _social_oob_headers(tctx, **kw)
+            return sx_response(await oob_page_sx(
                 oobs=oob_headers,
                 content=content,
             ))
         else:
-            header_rows = _social_full_headers(tctx, **kw)
-            return full_page_sx(tctx, header_rows=header_rows, content=content)
+            header_rows = await _social_full_headers(tctx, **kw)
+            return await full_page_sx(tctx, header_rows=header_rows, content=content)
 
     # -- Index ----------------------------------------------------------------