Emergency pause owner is hard-coded to a single deployer address

[Mosas2000]

contracts/market-core.clar hard-codes CONTRACT-OWNER to one principal and gates set-contract-paused with tx-sender == CONTRACT-OWNER.

Evidence:

• contracts/market-core.clar defines CONTRACT-OWNER as a fixed principal.
• set-contract-paused uses that constant directly for authorization.

Impact:

• The emergency pause switch is tied to one deployer address and cannot be reassigned without redeploying the contract.
• Any deployment from a different principal will not be able to pause the contract, which weakens the emergency-control story.

Reproduction:

1. Deploy the contract from a different account than the hard-coded principal.
2. Call set-contract-paused from the actual deployer.
3. The authorization check fails because it only accepts the baked-in address.

Priority: Medium

Suggested scope:
Make the owner configurable at deployment time or store an owner variable that can be managed intentionally, so emergency controls stay usable across redeployments.