Add governance mechanism to set_max_supply to prevent unlimited admin inflation

[DeFiVC]

What

The admin can call set_max_supply to increase the token supply cap to any value without governance, timelock, or any form of checks and balances.

Why

Combined with mint(), this means the admin can mint unlimited tokens at any time. A compromised admin key could inflate the token supply arbitrarily, destroying token value. This is a significant centralization risk for any production deployment.

Scope

• Add a governance mechanism (e.g., multi-sig requirement, timelock, or hard cap)
• Consider a maximum increase per call (e.g., cannot increase by more than 2x)
• Consider a timelock delay before changes take effect
• Document the chosen approach

Technical Context

• File: contracts/learn-token/src/lib.rs (lines ~453-464)
• set_max_supply currently only requires admin auth
• The supply cap directly affects tokenomics and user trust

Acceptance Criteria

• set_max_supply cannot be increased without additional safeguards
• The chosen governance mechanism is documented
• Tests verify the new constraints
• The approach is reasonable for the project's current stage (don't over-engineer)

[EstherIkechukwu]

I have gone through the description expect a pr in less than 12hrs

[GiftedGiftB]

Hi! I'd like to work on this issue. I have experience with Soroban/Stellar smart contracts and tokenomics safeguards.

My approach: modify set_max_supply in contracts/learn-token/src/lib.rs to add a timelock delay (proposal + execution after N ledgers) combined with a per-call increase cap (e.g., max 2x) to prevent instant unbounded inflation, keeping it reasonably simple for the project's current stage rather than adding a full multi-sig/DAO system. I'll document the chosen mechanism and rationale, and add tests verifying the cap and timelock constraints are enforced.

[EstherIkechukwu]

I have gone through the description expect a pr in less than 12hrs