docs: expand contract state machine wiki

[nightcityblade]

Fixes #828

Summary

• expand the contract state machine wiki article with the concrete loan states and transitions implemented in loan_manager
• add a Mermaid diagram, transition table, and notes on NFT seizure semantics and lending pool fund flow
• document the emitted events and caller expectations for each lifecycle transition

Testing

• basic documentation validation via Python assertions for required sections, states, and Mermaid block
• verified docs/wiki/contract-state-machine.md exists in the path referenced by docs/wiki/README.md

[ogazboiz]

closing for inactivity — this has been open ~4+ weeks with no contributor response after the last review. main has moved a lot since (Express 5 migration, contract changes, ~150 new issues filed). if you want to continue, open a fresh PR rebased on current main and I'll review it promptly.

join us on Telegram if you want to coordinate: https://t.me/+DOylgFv1jyJlNzM0