feat: protocol fee distributor with automatic reward splitting

[JamesEjembi]

Implements a protocol-level fee collection and distribution contract with four integrated modules:

FeeCollector

• — Accumulates fees from whitelisted collectors
• Configurable collector set managed by admin governance
• Prevents double-spend by tracking pending fees per period

FeeDistributor

• — Admin seals a period with a Merkle root
• — Claimants verify their allocation via Merkle proof
• Period rotates automatically when is called

SplitConfig

• Basis-point-based split ratios that must sum to 10,000
• Updated via by admin
• Validates no duplicate recipients, no zero bps, total == 10000

SweepHandler

• Unclaimed fees auto-eligible for sweep after ~90 days (518,400 ledgers)
• Admin-only sends unclaimed funds to treasury
• Swept periods are marked and cannot be re-claimed

Tests

12 tests covering initialization, auth, deposit, period close, claim (error paths), sweep deadlines, split validation, and getters.

Closes #62