wip: add post-flatpak window-chrome checks to release docs

Author: trin94

docs/releasing.md

@@ -84,6 +84,23 @@ These steps apply to the [mpvQC-flatpak](https://github.com/mpvqc/mpvQC-flatpak)
 
 Once the build succeeds, it will be automatically committed to the flatpak repository. Users will receive the new version via regular updates.
 
+### Manual verification after the Flatpak build
+
+The Linux window chrome (drop shadow, rounded corners, frameless resizing) is self-drawn and compositor-dependent, so CI cannot cover it. Install the freshly built Flatpak and verify both setups:
+
+#### Desktop environment (e.g. GNOME, KDE Plasma)
+
+- [ ] Drop shadow is drawn around the window and strengthens while it is focused
+- [ ] Corners are rounded (top corners and bottom-right; the video corner may stay square in the horizontal layout)
+- [ ] Menu bar, close button and footer hover highlights stay within the rounded corners
+- [ ] Maximize, fullscreen and back to normal land in the expected state (no flicker back to normal)
+- [ ] Window drags to the top edge and resizes from every edge and corner
+
+#### Tiling window manager (e.g. Sway, Hyprland, niri)
+
+- [ ] Window sits flush with no transparent margin and no drop shadow
+- [ ] Corners are square
+
 ## Post-release - Website Update
 
 - [ ] Screenshots updated