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, 0 insertions, 105 deletions

diff --git a/src/platform/linux_platform.h b/src/platform/linux_platform.h
deleted file mode 100644
index 1237c85..0000000
--- a/src/platform/linux_platform.h
+++ /dev/null
@@ -1,105 +0,0 @@
-#ifndef SRDWM_LINUX_PLATFORM_H
-#define SRDWM_LINUX_PLATFORM_H
-
-#include "platform.h"
-#include <memory>
-#include <string>
-
-// Forward declarations for X11
-#ifdef __linux__
-struct _XDisplay;
-typedef struct _XDisplay Display;
-typedef unsigned long SRDWindow;
-typedef unsigned long Atom;
-
-// Forward declarations for Wayland
-struct wl_display;
-struct wl_registry;
-struct wl_compositor;
-struct wl_shell;
-struct wl_seat;
-struct wl_keyboard;
-struct wl_pointer;
-#endif
-
-class LinuxPlatform : public Platform {
-public:
-    enum class Backend {
-        Auto,
-        X11,
-        Wayland
-    };
-
-    explicit LinuxPlatform(Backend backend = Backend::Auto);
-    ~LinuxPlatform() override;
-
-    // Platform interface implementation
-    bool initialize() override;
-    void shutdown() override;
-    
-    bool poll_events(std::vector<Event>& events) override;
-    void process_event(const Event& event) override;
-    
-    std::unique_ptr<SRDWindow> create_window(const std::string& title, int x, int y, int width, int height) override;
-    void destroy_window(SRDWindow* window) override;
-    void set_window_position(SRDWindow* window, int x, int y) override;
-    void set_window_size(SRDWindow* window, int width, int height) override;
-    void set_window_title(SRDWindow* window, const std::string& title) override;
-    void focus_window(SRDWindow* window) override;
-    void minimize_window(SRDWindow* window) override;
-    void maximize_window(SRDWindow* window) override;
-    void close_window(SRDWindow* window) override;
-    
-    std::vector<Monitor> get_monitors() override;
-    Monitor get_primary_monitor() override;
-    
-    void grab_keyboard() override;
-    void ungrab_keyboard() override;
-    void grab_pointer() override;
-    void ungrab_pointer() override;
-    
-    std::string get_platform_name() const override;
-    bool is_wayland() const override;
-    bool is_x11() const override;
-    bool is_windows() const override;
-    bool is_macos() const override;
-
-private:
-    Backend backend_;
-    bool initialized_;
-    
-    // X11 specific members
-    Display* x11_display_;
-    SRDWindow x11_root_;
-    Atom x11_wm_delete_window_;
-    Atom x11_wm_protocols_;
-    
-    // Wayland specific members
-    wl_display* wayland_display_;
-    wl_registry* wayland_registry_;
-    wl_compositor* wayland_compositor_;
-    wl_shell* wayland_shell_;
-    wl_seat* wayland_seat_;
-    wl_keyboard* wayland_keyboard_;
-    wl_pointer* wayland_pointer_;
-    
-    // Common members
-    std::vector<Monitor> monitors_;
-    
-    // Private methods
-    bool initialize_x11();
-    bool initialize_wayland();
-    void shutdown_x11();
-    void shutdown_wayland();
-    
-    bool detect_backend();
-    void setup_x11_atoms();
-    void setup_wayland_registry();
-    
-    // Event processing
-    void process_x11_event(XEvent& event, std::vector<Event>& events);
-    void process_wayland_event(wl_display* display, std::vector<Event>& events);
-};
-
-#endif // SRDWM_LINUX_PLATFORM_H
-