Implement JSON credential storage

- Add JSON format for storing Vault credentials
- Update save_credentials function to support both formats
- Save both .json and .txt files for compatibility
- Update test_docker.sh to use jq for reliable JSON parsing
- Improve key extraction for unseal operations
- Update .gitignore to exclude JSON credentials

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

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

.gitignore

@@ -13,6 +13,7 @@ Cargo.lock
 
 # Vault related files
 vault-credentials.txt
+vault-credentials.json
 vault-config/
 
 # Temporary test files