Security Caps & Merkle-based Claims

Summary

This PR combines two major smart contract epics to improve both security and distribution scaling without hitting gas or storage constraints.

Per-Account Redemption Cap: Added a daily limit (configurable) that prevents a single account from redeeming an excessive amount of funds.
Global Circuit Breaker: Introduced a global redemption window limit. If aggregate redemptions across all users exceed this cap within the window, the circuit breaker trips.
Auto-Pause: When the global circuit breaker trips, it automatically sets redeem_paused to true, stopping all further redemptions until an admin manually intervenes and unpauses.
Events & Errors: Added CircuitBreakerTripped event, along with typed errors PerAccountCapExceeded and GlobalCapExceeded.

Admin Root Publishing: Admins can now publish a single Merkle Root representing the distribution list (user, amount) using set_merkle_root.
User Claiming (O(log n)): Users provide their Merkle proof to the claim_merkle function. The contract verifies the proof against the stored root, ensuring that users can only claim their exact allocation.
Double-Claim Prevention: Added a tracking mechanism mapping each successfully claimed leaf hash to a boolean to prevent double-claiming.
Gas Costs Shifted: The gas cost of crediting is now correctly shifted to the end-users claiming the reward, keeping admin overhead minimal and scalable to millions of users.

Deployed locally and tested that exceeding per-account limit returns Error::PerAccountCapExceeded.
Tested the global circuit breaker threshold triggering an auto-pause of the contract.
Added a full suite of Rust tests with locally generated Merkle trees to verify valid and invalid proofs.
Attempting to claim twice with the same valid proof properly reverts with Error::AlreadyClaimed.

Closes #723 Closes #897