submission-receive: name the disallowed phrase in error + support link

422 response now reads "Your submission contains disallowed phrase X.
Please remove it and try again. Questions? Email
support@relevantmediaproperties.com." so PR firms know exactly what
tripped the filter without having to ask.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/app/api/submission-receive/route.ts

@@ -39,11 +39,17 @@ export async function POST(request: NextRequest) {
 
   // Editorial guardrail: reject anything mentioning a disallowed phrase
   // (competitor publications, banned exhibitors, etc.) before it ever lands
-  // in bb.native_articles.
+  // in bb.native_articles. The error names the specific phrase(s) so the
+  // submitter knows what to edit, and points them at support for context.
   const violations = await findViolations(`${title}\n${content}`);
   if (violations.length > 0) {
+    const phraseList = violations.map((v) => `"${v.phrase}"`).join(', ');
     return NextResponse.json(
-      { error: 'Submission rejected: contains disallowed phrases', violations },
+      {
+        error: `Your submission contains disallowed phrase${violations.length > 1 ? 's' : ''}: ${phraseList}. Please remove ${violations.length > 1 ? 'them' : 'it'} and try again. Questions? Email support@relevantmediaproperties.com.`,
+        violations,
+        support_email: 'support@relevantmediaproperties.com',
+      },
       { status: 422 },
     );
   }