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

README.md

@@ -1,3 +1,37 @@
 # Pell
 
-Lightweight Wayland Shell
+> A minimal widget based shell written in Rust, cause I do what I want
+
+## Configuration
+
+Pell reads `$XDG_CONFIG_HOME/pell/config.toml` (or `~/.config/pell/config.toml`).
+Every key is optional, and changes are applied live, within a second of saving.
+
+```toml
+[colors]
+background = "#1e1e2e"    # "#rrggbb" or "#rrggbbaa"
+foreground = "#cdd6f4"
+```
+
+## System tray
+
+Tray icons show in a notch at the top-right of the screen. Pell acts as the
+`org.kde.StatusNotifierWatcher` itself, so no other tray (like waybar's) can run
+alongside it; if one is already running, Pell starts without its tray.
+
+- Left click activates the app (or opens its menu), middle click is the
+  secondary action, right click opens the menu.
+- Icons must be PNG (pixel data from the app, or a PNG in the icon theme).
+  Others show as a placeholder dot.
+- Submenus are shown inline, indented, rather than as separate popups.
+- Apps started before Pell may need a restart to show up.
+
+## AI Disclosure
+
+This project makes use of AI assistance. Specifically:
+
+- **Optimisation**: AI tools are used to suggest performance and readability improvements to existing code.
+- **Code verification**: AI tools are used to review code, spot bugs, and cross-check behaviour against intended design.
+
+All AI-generated or AI-assisted suggestions are reviewed by a human before being merged. The author remains responsible for the content of this repository.
+