Fix market header ImportError and sx docs menu bar 3 OOB insertion

- market/sx/layouts.sx: Update ~market-header-auto macro to build nav
  from data fields via ~market-desktop-nav-from-data instead of
  expecting pre-built "desktop-nav" SxExpr (removed in Phase 9)
- shared/sx/primitives_io.py: Import _market_header_data instead of
  deleted _desktop_category_nav_sx, return individual data fields
- sx/sx/layouts.sx: Fix ~sx-section-layout-oob to use ~oob-header-sx
  for inserting sub-row into always-existing container div

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

shared/sx/primitives_io.py

@@ -876,10 +876,10 @@ async def _io_events_ticket_type_ctx(
 async def _io_market_header_ctx(
     args: list[Any], kwargs: dict[str, Any], ctx: RequestContext
 ) -> dict[str, Any]:
-    """``(market-header-ctx)`` → dict with market header values.
+    """``(market-header-ctx)`` → dict with market header data.
 
-    Pre-builds desktop-nav and mobile-nav as SxExpr strings using
-    the existing Python helper functions in sxc.pages.layouts.
+    Returns plain data (categories list, hrefs, flags) for the
+    ~market-header-auto macro. Mobile nav is pre-built as SxExpr.
     """
     from quart import g, url_for
     from shared.config import config as get_config
@@ -916,9 +916,9 @@ async def _io_market_header_ctx(
         "category_label": "",
     }
 
-    # Pre-build nav using existing helper functions (lazy import from market service)
-    from sxc.pages.layouts import _desktop_category_nav_sx, _mobile_nav_panel_sx
-    desktop_nav = _desktop_category_nav_sx(mini_ctx, categories, "", "#main-panel")
+    # Build header + mobile nav data via new data-driven helpers
+    from sxc.pages.layouts import _market_header_data, _mobile_nav_panel_sx
+    header_data = _market_header_data(mini_ctx)
     mobile_nav = _mobile_nav_panel_sx(mini_ctx)
 
     return {
@@ -926,7 +926,12 @@ async def _io_market_header_ctx(
         "link-href": link_href,
         "top-slug": "",
         "sub-slug": "",
-        "desktop-nav": SxExpr(desktop_nav) if desktop_nav else "",
+        "categories": header_data.get("categories", []),
+        "hx-select": header_data.get("hx-select", "#main-panel"),
+        "select-colours": header_data.get("select-colours", ""),
+        "all-href": header_data.get("all-href", ""),
+        "all-active": header_data.get("all-active", False),
+        "admin-href": header_data.get("admin-href", ""),
         "mobile-nav": SxExpr(mobile_nav) if mobile_nav else "",
     }