chore: downgrade claude-agent-sdk to 0.2.12

Downgrade @anthropic-ai/claude-agent-sdk from 0.2.17 to 0.2.12 to improve
Supply Chain Security score (from 73 to potentially higher based on Socket
Security analysis in PR vercel#117).

Author: k35o

package.json

@@ -40,7 +40,7 @@
     "zod": "4.3.6"
   },
   "devDependencies": {
-    "@anthropic-ai/claude-agent-sdk": "^0.2.17",
+    "@anthropic-ai/claude-agent-sdk": "^0.2.12",
     "@types/node": "^24.7.2",
     "dotenv": "^17.2.3",
     "typescript": "^5.9.2",