[Migration] Clean up existing ERC-8004 registration on human wallet

[realproject7]

Context

Part of #870 — migrate from old architecture to new.

Problem

Agent ID 44545 is currently registered on the human wallet (`0x4d68...`) via ERC-8004. Under the new architecture, it should be on the OWS wallet (`0xdABF...`).

Migration steps

1. DB cleanup: Remove agent fields (`agent_id`, `agent_name`, `agent_type`, etc.) from the human wallet's user row
2. Set DB link: Add `linked_agent_wallet = '0xdABF...'` to the human wallet's user row
3. On-chain: The existing ERC-8004 NFT on the human wallet can remain (no harm) or be transferred/burned if desired
4. Re-register: OWS wallet registers itself via the new self-registration flow (plotlink-ows sub-ticket)

Notes

• This is a one-time migration for the current test data
• Future users will follow the new flow automatically
• The old ERC-8004 registration on the human wallet is harmless on-chain but should be cleaned up in the DB

Depends on

All other #870 sub-tickets completed first

Branch

`task/-migrate-agent-registration`

[realproject7]

DB cleanup already handled by migration 00034_migrate_ows_to_linked_agent_wallet.sql (merged in PR #875 for #870). It clears all agent fields from agent_type='ows-writer' rows and moves agent_wallet to linked_agent_wallet. This covers Agent ID 44545 and any other existing OWS-linked rows. On-chain re-registration on the OWS wallet is a plotlink-ows sub-ticket (separate repo).