fix: Ctrl+R flip also matches the physical R key (v1.6.1)

On some keymaps the R key resolves to a different logical key (observed on a
Turkish remote-desktop setup: the R key arrives as logical T), so the Ctrl+R
shortcut never fired even though the key events reached the app. The shortcut
now matches PhysicalKeyboardKey.keyR as well; a regression test covers the
wrong-layout case.

README.md

@@ -18,8 +18,9 @@ Ultra-lightweight image viewer written in Flutter — Linux & Windows.
 - **Saturation:** Ctrl + Right drag + vertical move
 - **Brightness:** Ctrl+Shift + Right drag + vertical move
 - **Rotate:** Shift + Right drag + vertical move (~100px = 90°)
-- **Flip horizontally:** `R` — mirrors the view and clears the active effects (same reset as
-  double right click); press `R` again to undo
+- **Flip horizontally:** `Ctrl+R` — mirrors the view and clears the active effects (same reset as
+  double right click); press `Ctrl+R` again to undo. Also matches the physical R key position, so
+  keymaps that report the R key as a different character still work
 - **Reset (all effects):** Double right click
 - **Navigation arrows:** bottom corners, visible on hover
 - **Settings (gear):** sort by time/name, print, shortcut info
@@ -88,7 +89,7 @@ folder including `imajviewer.exe` and all DLLs).
 | Ctrl + Right drag + vertical | Saturation (0.0 – 2.0) |
 | Ctrl+Shift + Right drag + vertical | Brightness (-100 – 100) |
 | Shift + Right drag + vertical | Rotate (free) |
-| R | Flip horizontally (clears effects; press again to undo) |
+| Ctrl + R | Flip horizontally (clears effects; press again to undo) |
 | Double right click | Reset (all effects) |
 | Left / Right arrow | Previous / next image |
 | Ctrl + S | Save visible area (JPEG 93, original resolution) |