[Feat]: Make StoreFactory upgradeable (UUPS) so beacon ownership and user store bindings survive into R2

[re-gius]

Component

Store

Priority

P0

Summary

StoreFactory is the only non-upgradeable authority in the system (plain Ownable, contracts/store/StoreFactory.sol:28), yet it permanently holds:

1. Ownership of both store beacons: created in its constructor with no ownership-transfer path, so every futurecLabelStore/UserStore implementation upgrade depends forever on this one contract and its owner key. A lost or renounced key bricks the whole store fleet, unrecoverably.
2. The permanent user-to-store directory (_labelStores/_userStores): write-once, not migratable. Re-pointing the STORE_FACTORY registry key to a fresh factory would silently break label lookups and zero out transfer fees for all existing names.

Requirement: every R1 contract must have an owner-operated path to R2; StoreFactory currently does not.

Proposal

Convert StoreFactory to the same UUPS pattern as the other twelve contracts. The factory is then upgraded in place: bindings stay behind the proxy, beacon ownership sits with upgradeable logic, and both failure modes disappear.

Main requirements:

• Initializable + UUPSUpgradeable + OwnableUpgradeable, onlyOwner _authorizeUpgrade, __gap
• Beacons created in initialize, owned by the proxy; beacon addresses and protocolRegistry in storage instead of immutables
• Deploy pipeline switches the factory to the UUPS deploy path; verification and DEPLOYMENTS.md updated

Acceptance criteria

• StoreFactory behind an ERC1967 proxy, upgrade gated onlyOwner
• Both beacons owned by the proxy
• Existing behaviour unchanged (store deploy auth, claim, one-store-per-user)
• OZ upgrade-safety validation passes; deploy pipeline and docs updated