Implement two-step admin time-lock for protocol upgrades

[Code-Paragon]

Problem

The emergency_pause function contains a TODO for a time-lock mechanism. Instantly replacing an admin or upgrading protocol settings presents a centralization risk to LPs.

Expected behavior

The admin role logic is refactored into a two-step process: transfer_admin sets a pending admin, and accept_admin (callable only by the pending address) finalizes it.

Files to update

• src/lib.rs
• src/vault.rs
• src/test.rs

Project relevance

This drastically improves the non-custodial trust model by preventing the current admin from instantly and unilaterally compromising the Vault's governance.

Acceptance criteria

• Feature works as described
• Tests are added or updated where needed
• Documentation is updated where needed
• DataKey::PendingAdmin is added and validated during the acceptance step
• No TypeScript, lint, test, or build errors