Add cross-service URL functions and rights to base_context

blog_url, market_url, cart_url, events_url and g.rights were only
available as Jinja globals, not in the ctx dict passed to sexp
helper functions. This caused all cross-service links in the header
system (post title, cart badge, admin cog, admin nav items) to
produce relative URLs resolving to the current service domain.

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

shared/infrastructure/context.py

@@ -14,6 +14,7 @@ from quart import request, g, current_app
 from shared.config import config
 from shared.utils import host_url
 from shared.browser.app.utils import current_route_relative_path
+from shared.infrastructure.urls import blog_url, market_url, cart_url, events_url
 
 
 def _qs_filter_fn():
@@ -102,4 +103,9 @@ async def base_context() -> dict:
         "base_title": config()["title"],
         "hx_select": hx_select,
         "hx_select_search": hx_select_search,
+        "blog_url": blog_url,
+        "market_url": market_url,
+        "cart_url": cart_url,
+        "events_url": events_url,
+        "rights": getattr(g, "rights", {}),
     }