feat(events): markdown body, registered indicator, drop capacity counters

- Public event detail page renders description/series-description/content
  as markdown via useMarkdown, with prose styles; agenda becomes an
  unordered list with the same custom bullets.
- Events list API returns `isRegistered` per event (derived from the
  requester's registrations, ignoring cancelled rows), and the list page
  shows a "Registered" tag. Stops exposing the full registrations array
  in the list response.
- Removes the seats/sold-out/limited capacity UI from list and detail
  pages.
- EventTicketPurchase: minor template formatting (self-closing inputs,
  prettier wrapping).

server/api/events/index.get.js

@@ -35,17 +35,30 @@ export default defineEventHandler(async (event) => {
     }
 
     // Fetch events from database
-    const events = await Event.find(filter)
-      .sort({ startDate: 1 })
-      .select("-registrations") // Don't expose registration details in list view
-      .lean();
+    const events = await Event.find(filter).sort({ startDate: 1 }).lean();
 
-    // Add computed fields
-    const eventsWithMeta = events.map((event) => ({
-      ...event,
-      id: event._id.toString(),
-      registeredCount: event.registrations?.length || 0,
-    }));
+    const requesterEmail = requester?.email?.toLowerCase();
+    const requesterId = requester?._id?.toString();
+
+    // Add computed fields; strip registrations from the response.
+    const eventsWithMeta = events.map((event) => {
+      const regs = event.registrations || [];
+      const isRegistered =
+        !!requester &&
+        regs.some(
+          (r) =>
+            !r.cancelledAt &&
+            ((r.memberId && r.memberId.toString() === requesterId) ||
+              (r.email && r.email.toLowerCase() === requesterEmail)),
+        );
+      const { registrations, ...rest } = event;
+      return {
+        ...rest,
+        id: event._id.toString(),
+        registeredCount: regs.length,
+        isRegistered,
+      };
+    });
 
     return eventsWithMeta;
   } catch (error) {