[Mike] 01. Implement escrow state persistence

[Chucks1093]

Closes #51

Summary

• replace the inconsistent escrow placeholder implementation with a single persisted state model for escrow lifecycle and participant metadata
• persist escrow records with client and freelancer addresses, milestone state, funded and released accounting, lifecycle status, timestamps, and one-time reputation issuance tracking
• add persisted governance parameters and pause or emergency controls that survive across calls and guard state-changing payment flows
• add a dedicated persistence regression module plus updated lifecycle, governance, security, emergency, and performance coverage
• remove obsolete legacy test modules and tracked snapshot fixtures tied to the previous conflicting escrow test surface
• update reviewer documentation in the root README and docs/escrow/ with storage layout, invariants, and security assumptions

Security Notes

• contract creation requires authenticated client consent and rejects invalid participant or milestone metadata before any escrow state is stored
• funding is bounded so funded_amount cannot exceed total_amount
• milestone releases are one-way and require enough funded but unreleased balance to prevent double-release or balance bypass
• completed contracts grant one pending reputation credit to the recorded freelancer, and that credit is consumed exactly once when reputation is issued
• governance setup is single-use and governance admin transfer is two-step
• pause and emergency flags fail closed for all mutating escrow payment paths

Testing

• cargo fmt --all -- --check
• cargo test -p escrow

Notes

• tracked snapshot files from the old escrow test surface were removed because they no longer match the rewritten persistence-focused contract and test suite

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[Chucks1093]

@mikewheeleer can you please review and close this pr?

[mikewheeleer]

@Chucks1093 please resolve the conflicts