feat: add admin emergency pause

[dangelo352]

Summary

• add one-time initialize(admin) and admin-gated set_paused(paused)
• add ContractPaused, AlreadyInitialized, and NotInitialized errors
• gate create, validate, release, redirect, and cancel while preserving read-only getters
• emit paused / unpaused events and document the admin pause model
• add focused pause tests for round-trip pause/unpause, blocked mutating entrypoints, readable getters, double initialization, pre-init set_paused, and non-admin auth rejection

Tests

• cargo test --test pause -- --nocapture
• cargo test
• cargo clippy --all-targets --all-features -- -D warnings
• cargo fmt --check
• git diff --check

Closes #221

[1nonlypiece]

thanks for jumping on this. #221 hasn't been assigned to you though, and we need the PR author claimed on the issue before review. closing as invalid for now — grab #221 on the board and raise it again. https://discord.gg/xvNAvMJf