fix(ui): keep the Leave button reachable on a short window (A12)

The controls column (mute/deafen/PTT/echo/record/share/Leave) had no scroll,
so on a short window the bottom of it — including Leave — was clipped with no
way to reach it; the only workaround was enlarging the window. At a small
enough size you couldn't exit the call through the UI at all.

Fix: pin Leave at the bottom of the control panel and wrap the controls above
it in a scrollable (height Fill). The controls now scroll when the window is
too short, and Leave (the exit control) is always visible. Applies to all
three room layouts (control_panel is Fill-height in every arm).

Build + clippy clean. Manual check: create a room, shrink the window — Leave
stays put, controls scroll.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/mod.rs

@@ -1834,22 +1834,30 @@ fn view(state: &AppState) -> Element<'_, AppMessage> {
                     share_btn = share_btn.on_press(AppMessage::ToggleScreenShare);
                 }
                 share_btn
-            },
+            }
-            vertical_space(30.0),
+        ];
-            button(btn_content(IconKind::Leave, "Leave Room", color_crust))
+
+        // Leave is the exit control, so it's pinned below the scrolling controls
+        // (built separately, outside `ctrl_buttons`) — see the panel assembly (A12).
+        let leave_btn = button(btn_content(IconKind::Leave, "Leave Room", color_crust))
             .on_press(AppMessage::LeavePressed)
             .style(b_style(color_red, color_maroon, color_crust, 8.0))
             .padding(14)
-            .width(iced::Length::Fill)
+            .width(iced::Length::Fill);
-        ];
 
-        // Controls panel — width is set per layout below.
+        // Controls panel — width is set per layout below. The controls SCROLL when
+        // the window is too short, and Leave stays pinned at the bottom so the exit
+        // control is always reachable instead of being clipped off-screen (A12).
         let control_panel = container(
             column![
                 text("Controls").size(18).color(color_blue),
                 vertical_space(15.0),
-                ctrl_buttons,
+                scrollable(ctrl_buttons)
-                vertical_space(20.0),
+                    .width(iced::Length::Fill)
+                    .height(iced::Length::Fill),
+                vertical_space(12.0),
+                leave_btn,
+                vertical_space(8.0),
                 text(&state.status_message).size(12).color(color_subtext)
             ]
         )