Migrate all apps to defpage declarative page routes

Replace Python GET page handlers with declarative defpage definitions in .sx
files across all 8 apps (sx docs, orders, account, market, cart, federation,
events, blog). Each app now has sxc/pages/ with setup functions, layout
registrations, page helpers, and .sx defpage declarations.

Core infrastructure: add g I/O primitive, PageDef support for auth/layout/
data/content/filter/aside/menu slots, post_author auth level, and custom
layout registration. Remove ~1400 lines of render_*_page/render_*_oob
boilerplate. Update all endpoint references in routes, sx_components, and
templates to defpage_* naming.

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

shared/sx/layouts.py

@@ -16,6 +16,8 @@ from typing import Any, Callable, Awaitable
 from .helpers import (
     root_header_sx, post_header_sx, post_admin_header_sx,
     oob_header_sx, header_child_sx,
+    mobile_menu_sx, mobile_root_nav_sx,
+    post_mobile_nav_sx, post_admin_mobile_nav_sx,
 )
 
 
@@ -26,17 +28,19 @@ from .helpers import (
 class Layout:
     """A named layout that generates header rows for full and OOB rendering."""
 
-    __slots__ = ("name", "_full_fn", "_oob_fn")
+    __slots__ = ("name", "_full_fn", "_oob_fn", "_mobile_fn")
 
     def __init__(
         self,
         name: str,
         full_fn: Callable[..., str | Awaitable[str]],
         oob_fn: Callable[..., str | Awaitable[str]],
+        mobile_fn: Callable[..., str | Awaitable[str]] | None = None,
     ):
         self.name = name
         self._full_fn = full_fn
         self._oob_fn = oob_fn
+        self._mobile_fn = mobile_fn
 
     async def full_headers(self, ctx: dict, **kwargs: Any) -> str:
         result = self._full_fn(ctx, **kwargs)
@@ -50,6 +54,14 @@ class Layout:
             result = await result
         return result
 
+    async def mobile_menu(self, ctx: dict, **kwargs: Any) -> str:
+        if self._mobile_fn is None:
+            return ""
+        result = self._mobile_fn(ctx, **kwargs)
+        if hasattr(result, "__await__"):
+            result = await result
+        return result
+
     def __repr__(self) -> str:
         return f"<Layout:{self.name}>"
 
@@ -113,9 +125,27 @@ def _post_admin_oob(ctx: dict, **kw: Any) -> str:
     return "(<> " + post_hdr + " " + admin_oob + ")"
 
 
-register_layout(Layout("root", _root_full, _root_oob))
-register_layout(Layout("post", _post_full, _post_oob))
-register_layout(Layout("post-admin", _post_admin_full, _post_admin_oob))
+def _root_mobile(ctx: dict, **kw: Any) -> str:
+    return mobile_root_nav_sx(ctx)
+
+
+def _post_mobile(ctx: dict, **kw: Any) -> str:
+    return mobile_menu_sx(post_mobile_nav_sx(ctx), mobile_root_nav_sx(ctx))
+
+
+def _post_admin_mobile(ctx: dict, **kw: Any) -> str:
+    slug = ctx.get("post", {}).get("slug", "")
+    selected = kw.get("selected", "")
+    return mobile_menu_sx(
+        post_admin_mobile_nav_sx(ctx, slug, selected),
+        post_mobile_nav_sx(ctx),
+        mobile_root_nav_sx(ctx),
+    )
+
+
+register_layout(Layout("root", _root_full, _root_oob, _root_mobile))
+register_layout(Layout("post", _post_full, _post_oob, _post_mobile))
+register_layout(Layout("post-admin", _post_admin_full, _post_admin_oob, _post_admin_mobile))
 
 
 # ---------------------------------------------------------------------------
@@ -127,13 +157,15 @@ _CUSTOM_LAYOUTS: dict[str, tuple] = {}  # name → (full_fn, oob_fn)
 
 def register_custom_layout(name: str,
                            full_fn: Callable[..., str | Awaitable[str]],
-                           oob_fn: Callable[..., str | Awaitable[str]]) -> None:
+                           oob_fn: Callable[..., str | Awaitable[str]],
+                           mobile_fn: Callable[..., str | Awaitable[str]] | None = None) -> None:
     """Register a custom layout function.
 
     Used by services with non-standard header patterns::
 
         register_custom_layout("sx-section",
             full_fn=my_full_headers,
-            oob_fn=my_oob_headers)
+            oob_fn=my_oob_headers,
+            mobile_fn=my_mobile_menu)
     """
-    register_layout(Layout(name, full_fn, oob_fn))
+    register_layout(Layout(name, full_fn, oob_fn, mobile_fn))