fix(web): wanted POST converges on P2002 unique race instead of 500

Two concurrent Wants for the same release-group both pass the
findUnique existence check as absent; the loser's create() then hits
the rgMbid unique constraint and threw an uncaught P2002, 500ing the
request. Wrap the create in try/catch and fall back to the same
update-and-return-200 path on P2002, converging instead of erroring.
Non-P2002 errors are rethrown unchanged.

web/src/app/api/wanted/route.ts

@@ -1,3 +1,4 @@
+import { Prisma } from "@prisma/client";
 import { prisma } from "@/lib/db";
 import { searchReleaseGroup } from "@/lib/musicbrainz";
 
@@ -49,17 +50,29 @@ export async function POST(request: Request) {
     const updated = await prisma.monitoredRelease.update({ where: { rgMbid: match.rgMbid }, data: { monitored: true } });
     return Response.json({ id: updated.id, album: updated.album, monitored: updated.monitored }, { status: 200 });
   }
-  const created = await prisma.monitoredRelease.create({
-    data: {
-      artistMbid: match.artistMbid,
-      artistName: match.artistName,
-      rgMbid: match.rgMbid,
-      album: match.title,
-      primaryType: match.primaryType,
-      secondaryTypes: match.secondaryTypes,
-      firstReleaseDate: match.firstReleaseDate,
-      monitored: true,
-    },
-  });
-  return Response.json({ id: created.id, album: created.album, monitored: created.monitored }, { status: 201 });
+  try {
+    const created = await prisma.monitoredRelease.create({
+      data: {
+        artistMbid: match.artistMbid,
+        artistName: match.artistName,
+        rgMbid: match.rgMbid,
+        album: match.title,
+        primaryType: match.primaryType,
+        secondaryTypes: match.secondaryTypes,
+        firstReleaseDate: match.firstReleaseDate,
+        monitored: true,
+      },
+    });
+    return Response.json({ id: created.id, album: created.album, monitored: created.monitored }, { status: 201 });
+  } catch (e) {
+    if (e instanceof Prisma.PrismaClientKnownRequestError && e.code === "P2002") {
+      // Concurrent Want for the same release-group won the create; converge to the update path.
+      const updated = await prisma.monitoredRelease.update({
+        where: { rgMbid: match.rgMbid },
+        data: { monitored: true },
+      });
+      return Response.json({ id: updated.id, album: updated.album, monitored: updated.monitored }, { status: 200 });
+    }
+    throw e;
+  }
 }