feat(escrow): add two-step admin transfer

[BigMick03]

Closes #318

PR Request: Add Two-Step Governance Admin Transfer for Escrow

Summary

This PR adds a secure two-step admin transfer mechanism to the TalentTrust escrow governance layer in contracts/escrow.

What changed

• Implemented governance storage and management in contracts/escrow/src/governance.rs
• Added protocol parameter support and governance state keys in contracts/escrow/src/types.rs
• Updated contracts/escrow/src/lib.rs to expose governance functions and types
• Added/updated governance tests in contracts/escrow/src/test/governance.rs
• Clarified governance documentation in docs/escrow/governance-security.md

New public governance behavior

• initialize_protocol_governance(admin, ...) -> bool
• initialize_governance(admin) -> bool
• update_protocol_parameters(...) -> bool
• propose_governance_admin(new_admin) -> bool
• accept_governance_admin() -> bool
• get_protocol_parameters() -> ProtocolParameters
• get_governance_admin() -> Option<Address>
• get_pending_governance_admin() -> Option<Address>

Security model enforced

• Current governance admin must authenticate to propose a new admin
• Proposed admin must authenticate to accept transfer
• Pending admin state is cleared on acceptance
• A new proposal overwrites any existing pending admin
• Current admin retains control until the transfer is accepted

Files changed

• contracts/escrow/src/types.rs
• contracts/escrow/src/lib.rs
• contracts/escrow/src/governance.rs
• contracts/escrow/src/test/governance.rs
• contracts/escrow/src/test/mainnet_readiness.rs
• docs/escrow/governance-security.md

Test plan

Run locally in the repo root:

cargo fmt --all
cargo test -p escrow
cargo test -p escrow governance
cargo test test::performance -p escrow
cargo fmt --all -- --check

Notes

• This PR targets the escrow governance layer only.
• The implementation is intentionally scoped to the governance admin transfer flow and its supporting protocol parameter state.
• The document is written for reviewers and release notes.

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