Implement real `TaskClaim` validation — verify claimer capabilities

[iTranscend]

TaskClaim::validate() always returns Ok(()) without performing any actual validation. A node can claim tasks it is not capable of executing.

Location

src/message.rs, lines 49–57

impl Validate for TaskClaim {
    fn validate(&self) -> Result<(), Self::Error> {
        // TODO: validate claimer's capabilities
        println!("Validate taskClaim");
        Ok(())
    }
}