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/tickets/routes.py

@@ -127,7 +127,7 @@ def register() -> Blueprint:
         cart_count = summary.count + summary.calendar_count + summary.ticket_count
 
         from sx.sx_components import render_buy_result
-        return sx_response(render_buy_result(entry, created, remaining, cart_count))
+        return sx_response(await render_buy_result(entry, created, remaining, cart_count))
 
     @bp.post("/adjust/")
     @clear_cache(tag="calendars", tag_scope="all")
@@ -250,7 +250,7 @@ def register() -> Blueprint:
         cart_count = summary.count + summary.calendar_count + summary.ticket_count
 
         from sx.sx_components import render_adjust_response
-        return sx_response(render_adjust_response(
+        return sx_response(await render_adjust_response(
             entry, ticket_remaining, ticket_sold_count,
             user_ticket_count, user_ticket_counts_by_type, cart_count,
         ))