AI-06 browser test: end session returns header to normal #5

Verify that ending the guided session clears the guided UI and leaves the chat transcript intact.

Preconditions

• Guided session active (any progress state).

Steps

1. Click Sitzung beenden in the header.
2. Confirm inline: click Ja, beenden in the confirmation prompt.

Expected

• Header title reverts to KI-Assistent (without the - Gefuehrte Sitzung suffix).
• Progress pills disappear.
• Gefuehrte Sitzung starten, Profil teilen, and Leeren buttons are visible again in a single row.
• A system message Gefuehrte Sitzung beendet. appears at the bottom of the transcript.
• Previous messages remain in the transcript; user can continue chatting freely.

Also test

• Click Sitzung beenden then Weiter in the confirmation: confirmation closes, session stays active.
• Refresh the page while a guided session is active: transcript and session state are both cleared (ephemeral by design).

Reference

• Task: AI-06 (commit a825416)
• Ref file: src/features/ai-chat/ui/ChatView.tsx