URC-4 Standardizes Uniswap v4 Active Liquidity Hooks

URC-4 defines IALFHook, a router-facing interface for Uniswap v4 custom-accounting hooks. It standardizes getIndicativeQuote, isLive, maxGas, and swapToPrice functions. Hooks must emit HookSwap per URC-2. Two errors specified: MissingHookData and MalformedHookData. Extends URC-2, composable with URC-3. Status: Discussion.