fix: validation.rs require_positive_amount should panic with a message that includes the actual amount

[BigBen-7]

Description

require_positive_amount(e, amount) panics with "amount must be positive". The message does not include the actual invalid amount, making debugging harder.

What to fix

pub fn require_positive_amount(amount: i128) {
    if amount <= 0 {
        panic!("InvalidAmount: amount must be positive, got {}", amount);
    }
}

Update any tests that match on the old message string.

Files touched

• src/validation.rs
• Any test files matching the old panic string

PR requirement

• Closes #[issue_id] — Timeframe: 24 hours