gui: scroll the host body and grow the default window for the QR

The QR panel pushed the Stop hosting button below the fold at the old
520x480 default. Wraps host_running/host_form in a vertical ScrollArea
(header stays pinned) and bumps the initial height to 640 so the common
case fits without scrolling.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/gui/mod.rs

@@ -66,8 +66,11 @@ use winit::window::{Window, WindowAttributes, WindowId};
 use self::child::{ChildEvent, ChildProc};
 use self::tray::{TrayAction, TrayHandle, TrayStatus};
 
-/// Initial / minimum window size, in logical points.
-const INNER_SIZE: [f64; 2] = [520.0, 480.0];
+/// Initial / minimum window size, in logical points. Initial height fits the
+/// host screen (ticket + Copy + QR + Stop) without needing to scroll on a 1080p
+/// display; the host screen still wraps in a ScrollArea for the case where the
+/// user shrinks the window below MIN_INNER_SIZE proportions.
+const INNER_SIZE: [f64; 2] = [520.0, 640.0];
 const MIN_INNER_SIZE: [f64; 2] = [460.0, 380.0];
 
 /// Events delivered to the winit loop from off the UI thread (or from egui).
@@ -959,11 +962,16 @@ impl PixelPassApp {
         });
         ui.separator();
 
-        if running {
-            self.host_running(ui);
-        } else {
-            self.host_form(ui);
-        }
+        // Scroll the body, not the header — Menu/Host stay pinned at the top.
+        // Needed once the QR panel landed: ticket + Copy + QR + Stop overflows a
+        // shrunken window.
+        egui::ScrollArea::vertical().show(ui, |ui| {
+            if running {
+                self.host_running(ui);
+            } else {
+                self.host_form(ui);
+            }
+        });
     }
 
     fn host_form(&mut self, ui: &mut egui::Ui) {