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/calendar/admin/routes.py

@@ -19,7 +19,7 @@ def register():
     @require_admin
     async def calendar_description_edit(calendar_slug: str, **kwargs):
         from sx.sx_components import render_calendar_description_edit
-        html = render_calendar_description_edit(g.calendar)
+        html = await render_calendar_description_edit(g.calendar)
         return sx_response(html)
 
 
@@ -35,7 +35,7 @@ def register():
         await g.s.flush()
 
         from sx.sx_components import render_calendar_description
-        html = render_calendar_description(g.calendar, oob=True)
+        html = await render_calendar_description(g.calendar, oob=True)
         return sx_response(html)
 
 
@@ -43,7 +43,7 @@ def register():
     @require_admin
     async def calendar_description_view(calendar_slug: str, **kwargs):
         from sx.sx_components import render_calendar_description
-        html = render_calendar_description(g.calendar)
+        html = await render_calendar_description(g.calendar)
         return sx_response(html)
     
     return bp