History persistence (~/.ferrish_history)

[cdprice02]

Save command history to disk and load it when ferrish starts.

Behavior:

• Default path: ~/.ferrish_history (configurable via ShellCtx config)
• history -r <path> reads/appends history from a file
• history -w <path> writes the current history to a file
• Plain text format, one command per line
• Respect configurable maximum history size

Acceptance criteria:

• History persists across sessions
• history -r and history -w work correctly
• Max history size is enforced
• File path is configurable