Add display deletion endpoint and admin UI tweaks

app/routes/admin.py

@@ -498,3 +498,32 @@ def update_display_name(display_id: int):
     db.session.commit()
     flash("Display name updated", "success")
     return redirect(url_for("admin.company_detail", company_id=display.company_id))
+
+
+@bp.post("/displays/<int:display_id>/delete")
+@login_required
+def delete_display(display_id: int):
+    """Admin: delete a display."""
+
+    admin_required()
+
+    display = db.session.get(Display, display_id)
+    if not display:
+        abort(404)
+
+    company_id = display.company_id
+    display_name = display.name
+
+    # If FK constraints are enabled, delete in a safe order.
+    # 1) Unassign playlist
+    display.assigned_playlist_id = None
+
+    # 2) Delete active sessions for this display
+    DisplaySession.query.filter_by(display_id=display.id).delete(synchronize_session=False)
+
+    # 3) Delete display
+    db.session.delete(display)
+    db.session.commit()
+
+    flash(f"Display '{display_name}' deleted.", "success")
+    return redirect(url_for("admin.company_detail", company_id=company_id))