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/slots/routes.py

@@ -111,19 +111,19 @@ def register():
         # Success → re-render the slots table
         slots = await svc_list_slots(g.s, g.calendar.id)
         from sx.sx_components import render_slots_table
-        return sx_response(render_slots_table(slots, g.calendar))
+        return sx_response(await render_slots_table(slots, g.calendar))
 
         
     @bp.get("/add")
     @require_admin
     async def add_form(**kwargs):
         from sx.sx_components import render_slot_add_form
-        return sx_response(render_slot_add_form(g.calendar))
+        return sx_response(await render_slot_add_form(g.calendar))
 
     @bp.get("/add-button")
     @require_admin
     async def add_button(**kwargs):
         from sx.sx_components import render_slot_add_button
-        return sx_response(render_slot_add_button(g.calendar))
+        return sx_response(await render_slot_add_button(g.calendar))
 
     return bp