Persistent session name display and configurable prompt box border color

Feature Request

Problem

When using /rename to name a session, the session name and a blue/cyan prompt box border appear briefly as visual confirmation, then disappear. There's no way to persistently see which session you're in after that moment.

For users managing multiple concurrent sessions (e.g., across projects, worktrees, or parallel work tracks), having a persistent session identifier visible at all times would significantly improve orientation and reduce context-switching friction.

Proposed Solution

1. Persistent session name display — After /rename, keep the session name visible above or beside the prompt box for the duration of the session. This could be a subtle line like [session: my-session-name] above the input area.

1. Configurable prompt box border color — Allow users to set the prompt box border color via settings.json or tie it to the active agent's color frontmatter property. This would provide immediate visual context about which agent or mode is active.

Alternatives Considered

• Using hooks to inject session context — not possible since the prompt box rendering is internal to the Ink/React terminal UI layer
• Status line customization — partially addresses this but doesn't affect the prompt box itself

Additional Context

• The transient blue prompt box after /rename proves the UI already supports colored borders and text above the prompt — this request is to make that behavior persistent and configurable
• Users with complex agent orchestration setups (multiple named sessions across projects) would benefit most