docs: update screenshot tool reference to flameshot

The "Tooling" tables in README.md and ARCHITECTURE.md still listed
grim + slurp after the flameshot swap.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ARCHITECTURE.md

@@ -134,7 +134,7 @@ This system is a **Wayland-first desktop environment** built around the **Niri c
 | Function    | Tool         |
 | ----------- | ------------ |
 | Wallpaper   | swww         |
-| Screenshots | grim + slurp |
+| Screenshots | flameshot   |
 | Clipboard   | cliphist     |
 
 ---

README.md

@@ -13,7 +13,7 @@ A personal Wayland desktop configuration centered around the **Niri** tiling com
 | Lockscreen | gtklock |
 | Login/greeter | greetd + regreet |
 | Wallpaper | swww |
-| Screenshots | grim + slurp |
+| Screenshots | flameshot |
 | Clipboard | cliphist |
 | Theme | Tomorrow Night (GTK: Materia-dark, icons: Papirus) |