Add initial Wayland shell with clock and system tray

- Layer-shell bars drawn in software with tiny-skia and fontdue
- Clock widget centered at the top of the screen
- System tray in a top-right notch, acting as the
  StatusNotifierWatcher, with icons and right-click menus
- Live-reloaded TOML config for colors
  (~/.config/pell/config.toml)
- devenv setup for the Rust toolchain and Wayland libraries
- README: config, tray behaviour and AI disclosure

devenv.yaml

@@ -0,0 +1 @@
+# yaml-language-server: $schema=https://devenv.sh/devenv.schema.json