feat(daemon): support BSK_SESSION_IDLE and BSK_DAEMON_IDLE environment variables

[legend91019]

Summary

Fixes #456.

Make browser session idle timeout and daemon idle timeout configurable via \BSK_SESSION_IDLE\ and \BSK_DAEMON_IDLE\ environment variables.

Currently, --session-idle\ and --daemon-idle\ are only available as CLI arguments on explicit \�sk daemon start\ /
estart\ invocations. When \�sk\ subcommands auto-spawn a background daemon via \ensure_daemon(), the defaults (\5m\ session idle, \10m\ daemon idle) are always used with no way for users, container environments, or persistent supervisors to configure them globally.

Changes

1. Environment resolution fallback:
   • In \crates/bsk-cli/src/cli/daemon.rs,
     esolved_session_idle()\ and
     esolved_daemon_idle()\ check \BSK_SESSION_IDLE\ and \BSK_DAEMON_IDLE\ respectively before falling back to \DEFAULT_SESSION_IDLE\ (\5m) and \DEFAULT_DAEMON_IDLE\ (\10m).
2. Auto-spawn propagation:
   • In \crates/bsk-cli/src/cli/ensure_daemon.rs, \ensure_daemon()\ parses \BSK_SESSION_IDLE\ and \BSK_DAEMON_IDLE\ into \StartArgs\ so that \�pply_start_args()\ passes explicit --session-idle\ / --daemon-idle\ flags when spawning the background daemon process.
3. Explicit start resolution:
   • In \crates/bsk-cli/src/daemon/start.rs,
     un_start()\ populates unset idle timeouts from the environment variables.
4. Documentation:
   • Documented \BSK_SESSION_IDLE\ and \BSK_DAEMON_IDLE\ in \crates/bsk-cli/skill/references/environment.md.
5. Testing:
   • Added unit and CLI parsing tests in \crates/bsk-cli/tests/cli_parse.rs\ covering environment-based resolution, command-line flag precedence, default behavior, and fallback with test isolation.

Validation

• \cargo fmt --check: Passed (0 errors).
• \cargo test -p bsk --test cli_parse --locked: Passed (all 46 tests passed).
• \cargo test -p bsk daemon::sessions --locked: Passed.