Replace unsafe error handling with proper error propagation

[kwsantiago]

Description

• Found 1000+ instances of .expect() and .unwrap() that can crash the application
• These should use ? operator or proper error handling

Locations

• ddk-node/src/lib.rs:147 - Contract input deserialization
• ddk-node/src/command.rs:64,92,123,136 - JSON parsing
• Multiple other locations throughout codebase

Fix

• Replace with ? operator
• Add proper error context
• Return appropriate error types