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>

blog/sexp/sexp_components.py

@@ -16,6 +16,7 @@ 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 _shared_post_header_html,
+    post_admin_header_html as _shared_post_admin_header_html,
     oob_header_html,
     search_mobile_html, search_desktop_html,
     full_page, oob_page,
@@ -87,81 +88,9 @@ def _post_header_html(ctx: dict, *, oob: bool = False) -> str:
 # ---------------------------------------------------------------------------
 
 def _post_admin_header_html(ctx: dict, *, oob: bool = False, selected: str = "") -> str:
-    """Post admin header row with admin icon and nav links."""
-    from quart import url_for as qurl
-
-    post = ctx.get("post") or {}
-    slug = post.get("slug", "")
-    hx_select = ctx.get("hx_select_search", "#main-panel")
-    select_colours = ctx.get("select_colours", "")
-    styles = ctx.get("styles") or {}
-    nav_btn = styles.get("nav_button", "") if isinstance(styles, dict) else getattr(styles, "nav_button", "")
-
-    admin_href = qurl("blog.post.admin.admin", slug=slug)
-    label_html = render("blog-admin-label")
-    if selected:
-        label_html += f' <span class="text-white">{escape(selected)}</span>'
-
-    nav_html = _post_admin_nav_html(ctx, selected=selected)
-
-    return render("menu-row",
-        id="post-admin-row", level=2,
-        link_href=admin_href, link_label_html=label_html,
-        nav_html=nav_html, child_id="post-admin-header-child", oob=oob,
-    )
-
-
-def _post_admin_nav_html(ctx: dict, *, selected: str = "") -> str:
-    """Post admin desktop nav: calendars, markets, payments, entries, data, edit, settings."""
-    from quart import url_for as qurl
-
-    post = ctx.get("post") or {}
-    slug = post.get("slug", "")
-    hx_select = ctx.get("hx_select_search", "#main-panel")
-    select_colours = ctx.get("select_colours", "")
-    styles = ctx.get("styles") or {}
-    nav_btn = styles.get("nav_button", "") if isinstance(styles, dict) else getattr(styles, "nav_button", "")
-
-    # Base and selected class for nav items
-    base_cls = "justify-center cursor-pointer flex flex-row items-center gap-2 rounded bg-stone-200 text-black p-3"
-    selected_cls = "justify-center cursor-pointer flex flex-row items-center gap-2 rounded !bg-stone-500 !text-white p-3"
-
-    parts = []
-
-    # External links to events / market services
-    events_url_fn = ctx.get("events_url")
-    market_url_fn = ctx.get("market_url")
-    if callable(events_url_fn):
-        for url_fn, path, label in [
-            (events_url_fn, f"/{slug}/admin/", "calendars"),
-            (market_url_fn, f"/{slug}/admin/", "markets"),
-            (ctx.get("cart_url"), f"/{slug}/admin/payments/", "payments"),
-        ]:
-            if not callable(url_fn):
-                continue
-            href = url_fn(path)
-            cls = selected_cls if label == selected else (nav_btn or base_cls)
-            parts.append(render("blog-admin-nav-item",
-                href=href, nav_btn_class=cls, label=label,
-                select_colours=select_colours,
-            ))
-
-    # HTMX links
-    for endpoint, label in [
-        ("blog.post.admin.entries", "entries"),
-        ("blog.post.admin.data", "data"),
-        ("blog.post.admin.edit", "edit"),
-        ("blog.post.admin.settings", "settings"),
-    ]:
-        href = qurl(endpoint, slug=slug)
-        is_sel = label == selected
-        parts.append(render("nav-link",
-            href=href, label=label, select_colours=select_colours,
-            is_selected=is_sel,
-            aclass=(selected_cls + " " + select_colours) if is_sel else None,
-        ))
-
-    return "".join(parts)
+    """Post admin header row — delegates to shared helper."""
+    slug = (ctx.get("post") or {}).get("slug", "")
+    return _shared_post_admin_header_html(ctx, slug, oob=oob, selected=selected)
 
 
 # ---------------------------------------------------------------------------