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/all_events/routes.py

@@ -126,7 +126,7 @@ def register() -> Blueprint:
             frag_params["session_id"] = ident["session_id"]
 
         from sx.sx_components import render_ticket_widget
-        widget_html = render_ticket_widget(entry, qty, "/all-tickets/adjust")
+        widget_html = await render_ticket_widget(entry, qty, "/all-tickets/adjust")
         mini_html = await fetch_fragment("cart", "cart-mini", params=frag_params, required=False)
         return sx_response(widget_html + (mini_html or ""))