Remove render_to_sx from public API: enforce sx_call for all service code

Replace ~250 render_to_sx calls across all services with sync sx_call,
converting many async functions to sync where no other awaits remained.
Make render_to_sx/render_to_sx_with_env private (_render_to_sx).
Add (post-header-ctx) IO primitive and shared post/post-admin defmacros.
Convert built-in post/post-admin layouts from Python to register_sx_layout
with .sx defcomps. Remove dead post_admin_mobile_nav_sx.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

blog/bp/post/routes.py

@@ -106,7 +106,7 @@ def register():
   async def post_detail(slug: str):
     from shared.sx.page import get_template_context
     from shared.sx.helpers import (
-        render_to_sx, root_header_sx, full_page_sx, oob_page_sx,
+        sx_call, root_header_sx, full_page_sx, oob_page_sx,
         post_header_sx, oob_header_sx, mobile_menu_sx,
         post_mobile_nav_sx, mobile_root_nav_sx,
     )
@@ -124,9 +124,9 @@ def register():
     csrf = generate_csrf_token()
     svc = services.blog_page
     detail_data = svc.post_detail_data(post, user, rights, csrf, blog_url_base)
-    content = await render_to_sx("blog-post-detail-content", **detail_data)
+    content = sx_call("blog-post-detail-content", **detail_data)
     meta_data = svc.post_meta_data(post, tctx.get("base_title", ""))
-    meta = await render_to_sx("blog-meta", **meta_data)
+    meta = sx_call("blog-meta", **meta_data)
 
     if not is_htmx_request():
         root_hdr = await root_header_sx(tctx)
@@ -149,24 +149,24 @@ def register():
   @clear_cache(tag="post.post_detail", tag_scope="user")
   async def like_toggle(slug: str):
       from shared.utils import host_url
-      from shared.sx.helpers import render_to_sx
+      from shared.sx.helpers import sx_call
       from shared.browser.app.csrf import generate_csrf_token
 
       like_url = host_url(url_for('blog.post.like_toggle', slug=slug))
       csrf = generate_csrf_token()
 
-      async def _like_btn(liked):
+      def _like_btn(liked):
           if liked:
               colour, icon, label = "text-red-600", "fa-solid fa-heart", "Unlike this post"
           else:
               colour, icon, label = "text-stone-300", "fa-regular fa-heart", "Like this post"
-          return await render_to_sx("market-like-toggle-button",
+          return sx_call("market-like-toggle-button",
               colour=colour, action=like_url,
               hx_headers=f'{{"X-CSRFToken": "{csrf}"}}',
               label=label, icon_cls=icon)
 
       if not g.user:
-          return sx_response(await _like_btn(False), status=403)
+          return sx_response(_like_btn(False), status=403)
 
       post_id = g.post_data["post"]["id"]
       user_id = g.user.id
@@ -175,7 +175,7 @@ def register():
           "user_id": user_id, "target_type": "post", "target_id": post_id,
       })
 
-      return sx_response(await _like_btn(result["liked"]))
+      return sx_response(_like_btn(result["liked"]))
 
   @bp.get("/w/<widget_domain>/")
   async def widget_paginate(slug: str, widget_domain: str):