Background update check for deepagents-cli.
Compares the installed version against PyPI and caches the result
(see CACHE_TTL). All errors are silently swallowed to avoid disrupting
user experience.
Directory for user-level Deep Agents configuration (~/.deepagents).
Fetch the latest deepagents-cli version from PyPI, with caching.
Results are cached to CACHE_FILE to avoid repeated network calls.
Check whether a newer version of deepagents-cli is available.
