docs(readme): add testnet on-chain evidence: identity registry contract, deploy and seed txs, and the agent payment tx

[XxHugheadxX]

Summary

Adds an On-chain evidence (testnet) section to the README, as the Stellar Odyssey submission asks, and updates the Status list.

What	ID / hash
Agent Identity Registry contract (#13)	CD5QZOKGRBV35C5SDT6PG7S72XGG4BHQAC2L56YLNBJDUL4LDMTXFIJJ
Contract deployment	05724ac7c0c488ce3c24c93957814cee56c66f349807cf359ea8b4bc73171449
First demo agent registered (agent 0)	1499f85013ba2722991c1f0a04210101d7841bed444c928d933d07e041ac29f9
Last demo agent registered (agent 6)	4126614d1c16b0790c082e72cb76656cb7dffb6e5094dec98ec99cd4c219ea9f
Agent payment, SAC transfer with hire id 7 as muxed id (#7)	17ac14e085609df8e042b84e6c25aac7e1c30344eaa1b1fd0bcbed399b65243f

Each row links to stellar.expert. The section also gives two stellar contract invoke commands anyone can run to read the registry.

Status list: the Identity Registry, the verified payment and the domain model move to ✅; the Reputation Registry, the backend, the chain-wired app and agent execution stay 🚧.

Verification evidence

Every transaction checked with RPC getTransaction (xdrFormat: "json"):

05724ac7c0… SUCCESS  touches CD5QZOKG…                       (contract creation)
1499f85013… SUCCESS  touches CD5QZOKG…  event: registered     puls3://demo/payments-agent
4126614d1c… SUCCESS  touches CD5QZOKG…  event: registered     puls3://demo/analytics-agent
17ac14e085… SUCCESS                     event: transfer       (amount 5000000, to_muxed_id 7)

The README's CLI commands, run with an identity other than the deployer:

$ stellar contract invoke --id CD5QZOKG… --network testnet --source-account puls3-poc-payer -- total_agents
7
$ stellar contract invoke --id CD5QZOKG… --network testnet --source-account puls3-poc-payer -- agent_uri --agent-id 0
"puls3://demo/payments-agent"

All six stellar.expert links return HTTP 200; the relative links (ADR-0003, spikes/payments-poc/, puls3_domain/) resolve.

Notes for reviewers

The registry was deployed and seeded while reviewing #58, from its scripts on top of current main (so it includes the set_agent_uri TTL fix). contracts/deployments/testnet.json with this contract ID lands with #58.

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