fix: Remove duplicate sync:secrets script, keep sync-secrets as canonical

- Remove duplicate 'sync:secrets' script (line 41)
- Keep 'sync-secrets' (line 29) as the canonical version
- Matches existing references in bash scripts (clean-env-secrets.sh, pre-deploy-check.sh)
- Resolves DRY violation and script naming confusion

backend/package.json

@@ -37,8 +37,7 @@
     "test:watch": "vitest",
     "test:coverage": "vitest run --coverage",
     "test:pipeline": "ts-node src/scripts/test-complete-pipeline.ts",
-    "check:pipeline": "ts-node src/scripts/check-pipeline-readiness.ts",
-    "sync:secrets": "ts-node src/scripts/sync-firebase-secrets-to-env.ts"
+    "check:pipeline": "ts-node src/scripts/check-pipeline-readiness.ts"
   },
   "dependencies": {
     "@anthropic-ai/sdk": "^0.57.0",