Rewrite srdwm in Rust: working X11 and Wayland backends, Lua config

The C++ prototype (moved to legacy-cpp/) was mostly a design skeleton:
X11 and Windows backends were partially real, Wayland created the
wlroots object graph but never wired a single event listener, macOS
was stub except monitor enumeration, and the Lua engine's srd.bind()
stored a key-combo string but never the actual closure. See
docs/PRIOR_ART.md for the full audit.

This replaces it with a Cargo workspace:

- srdwm-core: platform-independent window/workspace/monitor state,
  a real master-stack tiling layout, and SmartPlacement grid/cascade/
  snap-to-edge placement - fixing several bugs in the C++ version
  (hardcoded 2-column grid, cascade that never cascaded, snap-to-edge
  that always returned a fixed rect). 35 unit tests.
- srdwm-config: the srd Lua API via mlua, implementing the surface
  docs/DEFAULTS.md always documented but the C++ engine never actually
  built (srd.window.close()/focus(direction), srd.workspace.next(),
  real keybinding closures, require("srd") support). 10 unit tests.
- srdwm-x11: a real reparenting WM with a drawn title bar (buttons,
  drag, resize), verified live under Xephyr - frame placement and
  client offset match srdwm-core's computed geometry exactly, and the
  decoration renders correctly on screen.
- srdwm-wayland: a from-scratch smithay compositor (the C++ version
  had nothing working to port from) - runs via the winit backend,
  tracks xdg-shell toplevels through the same WindowManager and
  hit-testing code X11 uses, verified to start/render/run without
  crashing. Decorations are solid-color (no text yet); see
  docs/IMPLEMENTATION_STATUS.md for exact scope.
- srdwm-windows / srdwm-macos: structured, cfg-gated designs informed
  by komorebi/glazewm and yabai/AeroSpace respectively (see
  docs/PRIOR_ART.md), honestly marked as unbuilt/unverified since this
  sandbox has no Windows or macOS target.

1 files changed, 63 insertions, 0 deletions

diff --git a/crates/core/src/event.rs b/crates/core/src/event.rs
new file mode 100644
index 0000000..9b464b5
--- /dev/null
+++ b/crates/core/src/event.rs
@@ -0,0 +1,63 @@
+use crate::monitor::{Monitor, MonitorId};
+use crate::window::WindowId;
+use bitflags::bitflags;
+
+bitflags! {
+    #[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
+    pub struct Modifiers: u8 {
+        const SHIFT = 0b0000_0001;
+        const CTRL  = 0b0000_0010;
+        const ALT   = 0b0000_0100;
+        const SUPER = 0b0000_1000;
+    }
+}
+
+impl std::fmt::Display for Modifiers {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        if self.contains(Modifiers::CTRL) {
+            write!(f, "Ctrl+")?;
+        }
+        if self.contains(Modifiers::SHIFT) {
+            write!(f, "Shift+")?;
+        }
+        if self.contains(Modifiers::ALT) {
+            write!(f, "Alt+")?;
+        }
+        if self.contains(Modifiers::SUPER) {
+            write!(f, "Mod4+")?;
+        }
+        Ok(())
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum MouseButton {
+    Left,
+    Right,
+    Middle,
+    Other(u8),
+}
+
+/// A key combination, e.g. "Mod4+Shift+Return", used both as the canonical
+/// string form for Lua keybindings and as the lookup key at dispatch time.
+pub fn key_combo_string(modifiers: Modifiers, key_name: &str) -> String {
+    format!("{modifiers}{key_name}")
+}
+
+#[derive(Debug, Clone)]
+pub enum Event {
+    WindowCreated(WindowId),
+    WindowDestroyed(WindowId),
+    WindowTitleChanged(WindowId, String),
+    WindowMoved { id: WindowId, x: i32, y: i32 },
+    WindowResized { id: WindowId, width: u32, height: u32 },
+    WindowFocused(WindowId),
+    WindowUnfocused(WindowId),
+    KeyPress { key_name: String, modifiers: Modifiers },
+    KeyRelease { key_name: String, modifiers: Modifiers },
+    MouseButtonPress { button: MouseButton, x: i32, y: i32 },
+    MouseButtonRelease { button: MouseButton, x: i32, y: i32 },
+    MouseMotion { x: i32, y: i32 },
+    MonitorAdded(Monitor),
+    MonitorRemoved(MonitorId),
+}