fix(market): guard execute_fee_rate_change with require_initialized

[Akeem813]

Problem

execute_fee_rate_change was the only state-mutating contract entry point that did not call validation::require_initialized before operating on persistent storage.

Every other mutating function (set_fee_rate, set_fee_cap, set_treasury, cancel_market, update_position, etc.) begins with require_initialized so callers on an uninitialized contract receive ContractError::NotInitialized rather than silently reading or writing orphaned storage entries.

Without the guard a caller could write FeeRateBps storage via execute_fee_rate_change before the contract admin is set — producing a partially-configured contract state inconsistent with the initialization invariant documented throughout the codebase.

What Changed

execute_fee_rate_change now opens with:

validation::require_initialized(&env)?;

This is the same guard used by every other mutating function. The existing timelock check (timestamp < effective_at → TimelockNotElapsed) is unchanged.

Files Changed

• contracts/market/src/lib.rs — add require_initialized as the first check in execute_fee_rate_change

Acceptance Criteria

• Early execute (before effective_at) fails with TimelockNotElapsed — existing check, unchanged
• Execute on uninitialized contract fails with NotInitialized — new guard
• Ready execute (after effective_at on initialized contract) updates FeeRateBps — existing behavior, unchanged