Rewrite moonlock from Python to Rust (v0.4.0)

Complete rewrite of the Wayland lockscreen from Python/PyGObject to
Rust/gtk4-rs for memory safety in security-critical PAM code and
consistency with the moonset/moongreet Rust ecosystem.

Modules: main, lockscreen, auth (PAM FFI), fingerprint (fprintd D-Bus),
config, i18n, users, power. 37 unit tests.

Security: PAM conversation callback with Zeroizing password, panic hook
that never unlocks, root check, ext-session-lock-v1 compositor policy,
absolute loginctl path, avatar symlink rejection.

Cargo.toml

@@ -0,0 +1,27 @@
+[package]
+name = "moonlock"
+version = "0.4.0"
+edition = "2024"
+description = "A secure Wayland lockscreen with GTK4, PAM and fingerprint support"
+license = "MIT"
+
+[dependencies]
+gtk4 = { version = "0.11", features = ["v4_10"] }
+gtk4-session-lock = { version = "0.4", features = ["v1_1"] }
+glib = "0.22"
+gdk4 = "0.11"
+gdk-pixbuf = "0.22"
+gio = "0.22"
+toml = "0.8"
+serde = { version = "1", features = ["derive"] }
+nix = { version = "0.29", features = ["user"] }
+zeroize = { version = "1", features = ["derive"] }
+libc = "0.2"
+log = "0.4"
+env_logger = "0.11"
+
+[dev-dependencies]
+tempfile = "3"
+
+[build-dependencies]
+glib-build-tools = "0.22"