Move calendar blueprint to app level for correct URL routing

The calendar blueprint was nested under calendars (admin), making URLs
/{slug}/admin/{calendar_slug}/ instead of /{slug}/{calendar_slug}/.

Register calendar blueprint directly on the app and update all endpoint
references from calendars.calendar.* to calendar.* (37 in Python,
~50 in templates).

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

events/bp/__init__.py

@@ -1,4 +1,5 @@
 from .all_events.routes import register as register_all_events
+from .calendar.routes import register as register_calendar
 from .calendars.routes import register as register_calendars
 from .markets.routes import register as register_markets
 from .payments.routes import register as register_payments

events/bp/calendars/routes.py

@@ -12,8 +12,6 @@ from .services.calendars import (
     create_calendar as svc_create_calendar,
 )
 
-from ..calendar.routes import register as register_calendar
-
 from shared.browser.app.redis_cacher import cache_page, clear_cache
 
 from shared.browser.app.authz import require_admin
@@ -22,9 +20,6 @@ from shared.browser.app.utils.htmx import is_htmx_request
 
 def register():
     bp = Blueprint("calendars", __name__, url_prefix='/admin')
-    bp.register_blueprint(
-      register_calendar(),
-    )
     @bp.context_processor
     async def inject_root():
         # Must always return a dict