feat: initial project with CPU-rendered ring light overlay

Wayland layer-shell overlay using tiny-skia for rendering a glowing
rounded rectangle ring. Includes PID-based lock file toggle via SIGUSR1,
keyboard capture (Escape to exit), and pointer tracking for cursor
avoidance. Configurable ring geometry and glow parameters.

Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "ringa"
+version = "0.1.0"
+edition = "2021"
+description = "Wayland ring light overlay"
+authors = ["Stephen Waits <steve@waits.net>"]
+rust-version = "1.85"
+
+[dependencies]
+anyhow = "1.0"
+nix = { version = "0.29", features = ["signal", "process", "poll"] }
+tempfile = "3"
+tiny-skia = "0.12.0"
+wayland-client = "0.31"
+wayland-protocols-wlr = { version = "0.3", features = ["client"] }