[jdjioe5-cpu]

Closes #8

Summary

The contract requires the administrator being installed to explicitly authorize assignment of control (\�dmin.require_auth()). This PR fulfills all acceptance criteria specified in #8 without breaking existing contract method signatures or deployment interfaces:

• Pins the front-running rejection behavior in a hermetic contract test using \mock_auths: an attacker proposing a target administrator with only attacker-owned credentials is unconditionally rejected by the host, ensuring an unauthorized caller cannot install an administrator it does not control.
• Verifies that only valid authorization from the intended administrator successfully initializes the vault and sets the administrator address.
• Asserts that subsequent re-initialization is strictly rejected with \VaultError::AlreadyInit\ regardless of caller authorization.
• Replaces outdated caveats in \docs/deployment/testnet.md\ with the accurate authorization guarantee while preserving the recommendation to initialize immediately upon creation.
• Documents the explicit \initialize\ authorization guarantee in \contracts/yield_vault/README.md.

Acceptance Criteria

• An unauthorized caller can no longer install an admin it does not control (\�dmin.require_auth())
• Contract test covers the front-running path and asserts rejection (\ est::initialize_rejects_front_runner_without_admin_auth)
• \cargo test -p yield_vault\ / \pnpm run contract:test\ passes (20/20 tests pass)
• \contracts/yield_vault/README.md\ and \docs/deployment/testnet.md\ reflect the new guarantee
• \cargo clippy -p yield_vault --all-targets -- -D warnings\ passes cleanly
• \pnpm run typecheck, \pnpm run lint, and \pnpm test\ pass across all workspace packages

Verification Evidence

\\�ash
$ cargo test -p yield_vault
running 20 tests
test test::initialize_rejects_front_runner_without_admin_auth ... ok
test test::authorization_is_required_for_initialization_users_and_admin ... ok
test test::initialization_validates_metadata_and_is_one_time ... ok
...
test result: ok. 20 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.31s

$ cargo clippy -p yield_vault --all-targets -- -D warnings
Finished \dev\ profile [unoptimized + debuginfo] target(s) in 0.52s

$ cargo fmt --all -- --check
Clean (exit code 0)

$ pnpm run typecheck && pnpm run lint
Clean (exit code 0)
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