feat: implement JMAP push notification handling and subscription management

app/api/push/register/[id]/route.ts

@@ -0,0 +1,29 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { logger } from '@/lib/logger';
+import { subscriptionStore } from '@/lib/push/store';
+import { isValidSubscriptionId } from '@/lib/push/validation';
+
+/**
+ * DELETE /api/push/register/:id
+ *
+ * Client tears down its relay mapping on logout / uninstall. Idempotent —
+ * deleting a non-existent id still returns ok.
+ */
+export async function DELETE(
+  _request: NextRequest,
+  { params }: { params: Promise<{ id: string }> },
+) {
+  try {
+    const { id } = await params;
+    if (!isValidSubscriptionId(id)) {
+      return NextResponse.json({ error: 'Invalid subscriptionId' }, { status: 400 });
+    }
+    await subscriptionStore.delete(id);
+    return NextResponse.json({ ok: true });
+  } catch (error) {
+    logger.error('push: unregister failed', {
+      error: error instanceof Error ? error.message : 'Unknown error',
+    });
+    return NextResponse.json({ error: 'Internal server error' }, { status: 500 });
+  }
+}