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>

shared/browser/templates/_types/root/_head.html

@@ -6,6 +6,7 @@
     <link rel="stylesheet" type="text/css" href="{{asset_url('styles/blog-content.css')}}">
     
     <script src="https://unpkg.com/htmx.org@2.0.8"></script>
+    <meta name="htmx-config" content='{"selfRequestsOnly":false}'>
     <script src="https://unpkg.com/hyperscript.org@0.9.12"></script>
     <script src="https://cdn.tailwindcss.com"></script>
     <link rel="stylesheet" href="{{asset_url('fontawesome/css/all.min.css')}}">