Fix ticket config update returning full page instead of fragment

The update_tickets route was rendering index.html (full page) but the
HTMX form targets #entry-tickets with innerHTML swap. Return just the
_tickets.html fragment instead.

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

bp/calendar_entry/routes.py

@@ -550,8 +550,8 @@ def register():
 
         await g.s.flush()
 
-        # Return updated entry view
-        html = await render_template("_types/entry/index.html")
+        # Return just the tickets fragment (targeted by hx-target="#entry-tickets-...")
+        html = await render_template("_types/entry/_tickets.html")
         return await make_response(html, 200)
 
     @bp.get("/posts/search/")