Auto-detect root password from IOM hostname on serial login

The BMC serial number (e.g. MXE3000048LHA03C) is embedded in the IOM
hostname shown in the serial login prompt. It also doubles as the root
password, so no manual entry is needed.

- If at login prompt: extract serial from 'hostname login:' line
- If already logged in: run 'hostname' on the shell and extract serial
- Falls back to prompt_password() if extraction fails either way

_login_serial_console() now returns (success, password) instead of bool.
Callers in workflow_serial.py and workflow_check.py updated accordingly.
CLAUDE.md updated to document the behaviour and remove it from planned features.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

modules/workflow_check.py

@@ -90,9 +90,8 @@ def _check_via_serial():
         return
 
     print()
-    password = prompt_password()
-
-    if not _login_serial_console(ser, password):
+    logged_in, password = _login_serial_console(ser)
+    if not logged_in:
         error("Could not log in to IOM console. Returning to main menu.")
         close_serial_connection(ser, device)
         time.sleep(2)