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/sexp/helpers.py

@@ -9,7 +9,7 @@ from __future__ import annotations
 from typing import Any
 
 from .jinja_bridge import sexp
-from .page import HAMBURGER_HTML, SEARCH_HEADERS_MOBILE, SEARCH_HEADERS_DESKTOP
+from .page import SEARCH_HEADERS_MOBILE, SEARCH_HEADERS_DESKTOP
 
 
 def call_url(ctx: dict, key: str, path: str = "/") -> str:
@@ -34,14 +34,13 @@ def root_header_html(ctx: dict, *, oob: bool = False) -> str:
     return sexp(
         '(~header-row :cart-mini-html cmi :blog-url bu :site-title st'
         ' :nav-tree-html nth :auth-menu-html amh :nav-panel-html nph'
-        ' :hamburger-html hh :oob oob)',
+        ' :oob oob)',
         cmi=ctx.get("cart_mini_html", ""),
         bu=call_url(ctx, "blog_url", ""),
         st=ctx.get("base_title", ""),
         nth=ctx.get("nav_tree_html", ""),
         amh=ctx.get("auth_menu_html", ""),
         nph=ctx.get("nav_panel_html", ""),
-        hh=HAMBURGER_HTML,
         oob=oob,
     )