fix: Initialize atp_uri and atp_cid variables for TypeScript strict mode

- Initialize atp_uri and atp_cid with empty strings to satisfy TypeScript strict mode
- Resolves "variable used before being assigned" compilation error

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/api/nodes/route.ts

@@ -47,8 +47,8 @@ export async function POST(request: NextRequest) {
   const detailUrl = `${process.env.NEXT_PUBLIC_APP_URL || 'https://ponderants.app'}/galaxy/${encodeURIComponent(nodeId)}`;
 
   // --- Step 1: Write to Source of Truth (ATproto) ---
-  let atp_uri: string;
-  let atp_cid: string;
+  let atp_uri = '';
+  let atp_cid = '';
 
   try {
     // Get the OAuth client and restore the user's session