Unify post admin nav across all services

Move post admin header into shared/sexp/helpers.py so blog, cart,
events, and market all render the same admin row with identical nav:
calendars | markets | payments | entries | data | edit | settings.

All links are external (cross-service). The selected item shows
highlighted on the right and as white text next to "admin" on the left.

- blog: delegates to shared helper, removes blog-specific nav builder
- cart: delegates to shared helper for payments admin
- events: adds shared admin row (selected=calendars) to calendar admin
- market: adds /<slug>/admin/ route + page_admin blueprint, delegates
  to shared helper (selected=markets). Fixes 404 on page-level admin.

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

market/sexp/sexp_components.py

@@ -15,6 +15,7 @@ from shared.sexp.jinja_bridge import render, load_service_components
 from shared.sexp.helpers import (
     call_url, get_asset_url, root_header_html,
     post_header_html as _post_header_html,
+    post_admin_header_html,
     oob_header_html as _oob_header_html,
     search_mobile_html, search_desktop_html,
     full_page, oob_page,
@@ -1420,7 +1421,7 @@ async def render_market_admin_page(ctx: dict) -> str:
     content = "market admin"
 
     hdr = root_header_html(ctx)
-    child = _post_header_html(ctx) + _market_header_html(ctx) + _market_admin_header_html(ctx)
+    child = _post_header_html(ctx) + _market_header_html(ctx) + _market_admin_header_html(ctx, selected="markets")
     hdr += render("header-child", inner_html=child)
     return full_page(ctx, header_rows_html=hdr, content_html=content)
 
@@ -1431,21 +1432,37 @@ async def render_market_admin_oob(ctx: dict) -> str:
 
     oobs = _market_header_html(ctx, oob=True)
     oobs += _oob_header_html("market-header-child", "market-admin-header-child",
-                              _market_admin_header_html(ctx))
+                              _market_admin_header_html(ctx, selected="markets"))
     return oob_page(ctx, oobs_html=oobs, content_html=content)
 
 
-def _market_admin_header_html(ctx: dict, *, oob: bool = False) -> str:
-    """Build market admin header row."""
-    from quart import url_for
+def _market_admin_header_html(ctx: dict, *, oob: bool = False, selected: str = "") -> str:
+    """Build market admin header row — delegates to shared helper."""
+    slug = (ctx.get("post") or {}).get("slug", "")
+    return post_admin_header_html(ctx, slug, oob=oob, selected=selected)
 
-    link_href = url_for("market.admin.admin")
-    return render(
-        "menu-row",
-        id="market-admin-row", level=3,
-        link_href=link_href, link_label="admin", icon="fa fa-cog",
-        child_id="market-admin-header-child", oob=oob,
-    )
+
+# ---------------------------------------------------------------------------
+# Page admin (/<slug>/admin/) — post-level admin for markets
+# ---------------------------------------------------------------------------
+
+async def render_page_admin_page(ctx: dict) -> str:
+    """Full page: page-level market admin."""
+    slug = (ctx.get("post") or {}).get("slug", "")
+    admin_hdr = post_admin_header_html(ctx, slug, selected="markets")
+    hdr = root_header_html(ctx)
+    child = _post_header_html(ctx) + admin_hdr
+    hdr += render("header-child", inner_html=child)
+    content = '<div id="main-panel"><div class="p-4 text-stone-500">Market admin</div></div>'
+    return full_page(ctx, header_rows_html=hdr, content_html=content)
+
+
+async def render_page_admin_oob(ctx: dict) -> str:
+    """OOB response: page-level market admin."""
+    slug = (ctx.get("post") or {}).get("slug", "")
+    oobs = post_admin_header_html(ctx, slug, oob=True, selected="markets")
+    content = '<div id="main-panel"><div class="p-4 text-stone-500">Market admin</div></div>'
+    return oob_page(ctx, oobs_html=oobs, content_html=content)
 
 
 # ---------------------------------------------------------------------------