Fix market and calendar URL routing

Market: blog links now use market_url('/{slug}/') instead of
events_url('/{slug}/markets/'), matching the market service's
actual route structure /<page_slug>/<market_slug>/.

Calendar: flatten route from /<slug>/calendars/<calendar_slug>/
to /<slug>/<calendar_slug>/ by changing the events app blueprint
prefix and moving listing routes to explicit /calendars/ paths.
Update all hardcoded calendar URL paths across blog and events
services (Python + Jinja templates).

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

events/bp/fragments/routes.py

@@ -58,7 +58,7 @@ def register():
             )
             for entry in entries:
                 entry_path = (
-                    f"/{post_slug}/calendars/{entry.calendar_slug}/"
+                    f"/{post_slug}/{entry.calendar_slug}/"
                     f"{entry.start_at.year}/{entry.start_at.month}/"
                     f"{entry.start_at.day}/entries/{entry.id}/"
                 )
@@ -87,7 +87,7 @@ def register():
                 g.s, container_type, container_id,
             )
             for cal in calendars:
-                href = events_url(f"/{post_slug}/calendars/{cal.slug}/")
+                href = events_url(f"/{post_slug}/{cal.slug}/")
                 html_parts.append(render_sexp(
                     '(~calendar-link-nav :href href :name name :nav-class nav-class)',
                     href=href, name=cal.name, **{"nav-class": nav_class},