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>

federation/bp/social/routes.py

@@ -156,7 +156,7 @@ def register(url_prefix="/social"):
         else:
             list_type = "following"
         from sx.sx_components import render_actor_card
-        return sx_response(render_actor_card(remote_dto, actor, followed_urls, list_type=list_type))
+        return sx_response(await render_actor_card(remote_dto, actor, followed_urls, list_type=list_type))
 
     # -- Interactions ----------------------------------------------------------
 
@@ -243,7 +243,7 @@ def register(url_prefix="/social"):
             )).scalar())
 
         from sx.sx_components import render_interaction_buttons
-        return sx_response(render_interaction_buttons(
+        return sx_response(await render_interaction_buttons(
             object_id=object_id,
             author_inbox=author_inbox,
             like_count=like_count,