Add option to scope Up arrow history to current session

Feature Request

Current behavior: Pressing the Up arrow key cycles through prompts from all previous sessions (per working directory). The history persists across sessions.

Desired behavior: An option/setting to make the Up arrow key only cycle through prompts sent in the current session/chat, rather than showing the full system-wide (per-directory) history.

Use Case

When starting a new session, pressing Up often surfaces old prompts from previous sessions that are no longer relevant. It would be helpful to have a configuration option (e.g., history.scope: "session" | "directory") to control whether prompt history is scoped to the current session or persists across sessions as it does today.

Suggested Approach

• Add a setting to control history scope (default could remain as-is for backwards compatibility)
• When set to session, only prompts entered in the current session would appear when pressing Up
• /clear would continue to reset history regardless of the setting