mark active account in list output

[vosslab]

Problem: codex-accounts.sh list did not indicate which account is currently active.

Change: cmd_list now calls load_state and prefixes the active account with "*". Non-active accounts continue to use "-".

User impact: Easier to confirm the active account at a glance. No change to account selection logic.

Before:

codex-accounts.sh list
- accountA
- accountB

After:

codex-accounts.sh list
* accountA
- accountB

Testing:

• Ran codex-accounts.sh list with a known active account set and confirmed "*" appears only on the active one.
• Ran codex-accounts.sh list with no saved accounts and confirmed output remains "(no accounts saved yet)".