fix(events): surface series-pass-required in ticket availability response

When a series requires a pass and doesn't allow drop-ins, the
per-event availability endpoint returned a generic "No tickets
available" reason, leaving the UI to render an "Event Sold Out"
block for guests (logged-in users short-circuit via
check-series-access first).

Detect the gate server-side and return
{available:false, reason:"series_pass_required", requiresSeriesPass:true,
series:{id,title,slug}} so EventTicketPurchase's existing
requiresSeriesPass branch renders a pass-required CTA with a link to
the series page. The register and purchase handlers already enforce
the gate server-side; this is a messaging fix only.

server/api/events/[id]/tickets/available.get.js

@@ -1,8 +1,10 @@
 import Member from "../../../../models/member.js";
+import Series from "../../../../models/series.js";
 import { loadPublicEvent } from "../../../../utils/loadEvent.js";
 import {
   calculateTicketPrice,
   checkTicketAvailability,
+  checkUserSeriesPass,
   formatPrice,
 } from "../../../../utils/tickets.js";
 
@@ -34,6 +36,36 @@ export default defineEventHandler(async (event) => {
       return { available: false, reason: "Registration deadline has passed" };
     }
 
+    // Series-pass gate: when an event is linked to a series that requires a
+    // pass and doesn't allow drop-ins, surface a structured response so the UI
+    // can route to the series page instead of rendering a generic "Sold Out"
+    // block. The register/purchase handlers enforce this gate independently.
+    if (
+      eventData.tickets?.requiresSeriesTicket &&
+      eventData.tickets?.seriesTicketReference
+    ) {
+      const series = await Series.findById(
+        eventData.tickets.seriesTicketReference,
+      );
+      if (series && !series.tickets?.allowIndividualEventTickets) {
+        const hasPass = userEmail
+          ? checkUserSeriesPass(series, userEmail).hasPass
+          : false;
+        if (!hasPass) {
+          return {
+            available: false,
+            reason: "series_pass_required",
+            requiresSeriesPass: true,
+            series: {
+              id: series.id,
+              title: series.title,
+              slug: series.slug,
+            },
+          };
+        }
+      }
+    }
+
     let member = null;
     if (userEmail) {
       member = await Member.findOne({ email: userEmail.toLowerCase() });