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, 33 insertions, 0 deletions

diff --git a/legacy-cpp/src/layouts/layout.h b/legacy-cpp/src/layouts/layout.h
new file mode 100644
index 0000000..00c002f
--- /dev/null
+++ b/legacy-cpp/src/layouts/layout.h
@@ -0,0 +1,33 @@
+#ifndef SRDWM_LAYOUT_H
+#define SRDWM_LAYOUT_H
+
+#include <vector>
+#include "../core/window.h"
+
+struct Monitor {
+    int id;
+    int x;
+    int y;
+    int width;
+    int height;
+    std::string name;
+    int refresh_rate;
+    
+    Monitor() : id(0), x(0), y(0), width(0), height(0), refresh_rate(60) {}
+    Monitor(int id, int x, int y, int width, int height, const std::string& name = "", int refresh = 60)
+        : id(id), x(x), y(y), width(width), height(height), name(name), refresh_rate(refresh) {}
+};
+
+class Layout {
+public:
+    virtual ~Layout() = default;
+
+    // Pure virtual method to arrange windows on a given monitor
+    virtual void arrange_windows(const std::vector<SRDWindow*>& windows, const Monitor& monitor) = 0;
+
+    // You might add other common layout methods here later, e.g.:
+    // virtual void add_window(SRDWindow* window) = 0;
+    // virtual void remove_window(SRDWindow* window) = 0;
+};
+
+#endif // SRDWM_LAYOUT_H