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>

likes/bp/data/routes.py

@@ -31,7 +31,7 @@ def register() -> Blueprint:
     async def _is_liked():
         """Check if a user has liked a specific target."""
         from sqlalchemy import select
-        from likes.models.like import Like
+        from models.like import Like
 
         user_id = request.args.get("user_id", type=int)
         target_type = request.args.get("target_type", "")
@@ -62,7 +62,7 @@ def register() -> Blueprint:
     async def _liked_slugs():
         """Return all liked target_slugs for a user + target_type."""
         from sqlalchemy import select
-        from likes.models.like import Like
+        from models.like import Like
 
         user_id = request.args.get("user_id", type=int)
         target_type = request.args.get("target_type", "")
@@ -86,7 +86,7 @@ def register() -> Blueprint:
     async def _liked_ids():
         """Return all liked target_ids for a user + target_type."""
         from sqlalchemy import select
-        from likes.models.like import Like
+        from models.like import Like
 
         user_id = request.args.get("user_id", type=int)
         target_type = request.args.get("target_type", "")