feat: add max_supply() view — return the configured token supply cap (0 if unlimited)

[BigBen-7]

Description

initialize_with_max_supply sets a cap but there is no public view to read it back. The SDK needs this to display whether the token has a supply cap and what it is.

What to do

Confirm max_supply(e: Env) -> i128 exists in contract.rs. If missing, add it:

pub fn max_supply(e: Env) -> i128 {
    e.storage().instance().get(&DataKey::MaxSupply).unwrap_or(0i128)
}

Add tests: returns 0 when no cap set, returns the configured cap when set.

Files touched

• src/contract.rs
• src/test.rs

PR requirement

• Closes #[issue_id] — Timeframe: 24 hours