feat(contracts): implement anti-mev protection, bounty board, dynamic drm licensing, and reputation decay

[adeniran19-maker]

Summary of Changes

This PR resolves issues #1656, #1657, #1661, and #1662 across the smart contract suite.

1. [SC-035] Anti-MEV Sandwich Protection (Closes #1656)

• Created contracts/amm/src/anti_mev.rs adding user-defined deadline verification (DeadlineExceeded), strict minimum output slippage checks, and same-block bidirectional trade restriction (SameBlockBidirectionalTrade).
• Integrated tracking in storage with DataKey::TradeRecord(Address).
• Added AMM unit tests and updated property/fuzz tests in tests/fuzz_amm.rs.

2. [SC-036] Decentralized Bounty Board (Closes #1657)

• Created contracts/freelance-platform/src/bounty.rs supporting bounty creation, escrow locking, single contributor milestone claims, and multi-contributor collaborative claims with split basis points summing to 10,000.
• Implemented verify_and_payout with proportional payouts and claim_refund granting 100% funder refunds after expiration.
• Added comprehensive unit tests covering single and split payouts, plus expired refunds.

3. [SC-040] Dynamic Licensing & DRM Contract (Closes #1661)

• Created contracts/content_management_system/src/drm.rs for on-chain curriculum copyright registration.
• Created contracts/content_management_system/src/licensing.rs for setting license terms, minting time-limited cryptographic license vouchers, directly forwarding royalty payments to course authors, and providing is_license_valid check and revocation support.
• Added full unit test coverage.

4. [SC-041] Decentralized Reputation Scoring with Decaying Trust (Closes #1662)

• Created contracts/sybil_resistance/src/decay.rs implementing exponential time decay formula without floating point arithmetic (R_t = R_0 * 2^(-t / T)) over 6-month epochs (180 days).
• Created contracts/sybil_resistance/src/reputation.rs capping scores at 10,000, supporting reputation increments with transparent reasoning codes (CourseCompletion, PeerReview, HackathonWin, TimeDecay, AdminAdjustment), and emitting audit events.
• Added tests validating score capping, exact halving, and fractional decay.

Verification

All 64 tests across all 4 touched packages passed cleanly:

• amm: 22 unit tests + 2 fuzz tests passing
• content-management-system: 23 unit tests passing
• freelance-platform: 10 unit tests passing
• sybil-resistance: 7 unit tests passing

Closes #1656
Closes #1657
Closes #1661
Closes #1662

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