Notify af users about newer CLI versions

[HappyDevs1]

Summary

• add a cached, best-effort update notice for interactive af commands
• skip checks in CI, non-TTY sessions, containers, and explicit update runs
• keep update checks advisory so network/cache failures do not affect commands

Fixes #140

Tests

• deno fmt --check packages/cli/update_check.ts packages/cli/update_check_test.ts packages/cli/main.ts
• deno lint packages/cli/update_check.ts packages/cli/update_check_test.ts packages/cli/main.ts
• deno task check
• deno test --allow-read --allow-write --allow-env --allow-run=bash --allow-net=127.0.0.1,0.0.0.0 packages/cli