[contracts] Define Rootfield ownership transfer and recovery policy

[FlowmemoryAI]

Objective

Define whether and how Rootfield ownership can transfer, recover, or rotate before adding any ownership mutation logic.

Context

RootfieldRegistry v0 assigns the registering account as owner and only that owner may submit roots. It does not implement ownership transfer, recovery, multisig assumptions, or governance controls.

Scope

• Document transfer and recovery options.
• Identify security risks around compromised keys and abandoned rootfields.
• Do not add upgrade systems, tokenomics, or production deployment logic.

Acceptance Criteria

• Accepted policy or open decision points are documented.
• Any future contract changes are split into a separate implementation issue with tests.