Enable cross-subdomain htmx and purify layout to sexp

- Disable htmx selfRequestsOnly, add CORS headers for *.rose-ash.com
- Remove same-origin guards from ~menu-row and ~nav-link htmx attrs
- Convert ~app-layout from string-concatenated HTML to pure sexp tree
- Extract ~app-head component, replace ~app-shell with inline structure
- Convert hamburger SVG from Python HTML constant to ~hamburger sexp component
- Fix cross-domain fragment URLs (events_url, market_url)
- Fix starts-with? primitive to handle nil values
- Fix duplicate admin menu rows on OOB swaps
- Add calendar admin nav links (slots, description)
- Convert slots page from Jinja to sexp rendering
- Disable page caching in development mode
- Backfill migration to clean orphaned container_relations

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

blog/sexp/sexp_components.py

@@ -86,19 +86,21 @@ def _post_header_html(ctx: dict, *, oob: bool = False) -> str:
         )
 
     # Admin link
-    from quart import url_for as qurl, g
+    from quart import url_for as qurl, g, request
     rights = ctx.get("rights") or {}
     has_admin = rights.get("admin") if isinstance(rights, dict) else getattr(rights, "admin", False)
     if has_admin:
-        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)
+        is_admin_page = "/admin" in request.path
+        sel_attr = ' aria-selected="true"' if is_admin_page else ''
         nav_parts.append(
             f'<div class="relative nav-group"><a href="{admin_href}"'
-            f' hx-get="{admin_href}" hx-target="#main-panel" hx-select="{hx_select}"'
+            f' hx-get="{admin_href}" hx-target="#main-panel" hx-select="#main-panel"'
             f' hx-swap="outerHTML" hx-push-url="true"'
+            f'{sel_attr}'
             f' class="{nav_btn} {select_colours}">'
             f'<i class="fa fa-cog" aria-hidden="true"></i></a></div>'
         )