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>

events/bp/calendars/routes.py

@@ -69,7 +69,7 @@ def register():
         from shared.sx.page import get_template_context
         from sx.sx_components import render_calendars_list_panel
         ctx = await get_template_context()
-        html = render_calendars_list_panel(ctx)
+        html = await render_calendars_list_panel(ctx)
 
         # Blog-embedded mode: also update post nav
         if post_data:
@@ -85,7 +85,7 @@ def register():
             ).scalars().all()
 
             associated_entries = await get_associated_entries(post_id)
-            nav_oob = render_post_nav_entries_oob(associated_entries, cals, post_data["post"])
+            nav_oob = await render_post_nav_entries_oob(associated_entries, cals, post_data["post"])
             html = html + nav_oob
 
         return sx_response(html)