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, 27 deletions

diff --git a/cmake/toolchains/mingw-w64-x86_64.cmake b/cmake/toolchains/mingw-w64-x86_64.cmake
deleted file mode 100644
index 7935b7e..0000000
--- a/cmake/toolchains/mingw-w64-x86_64.cmake
+++ /dev/null
@@ -1,27 +0,0 @@
-# MinGW-w64 x86_64 toolchain file for cross-compiling Windows binaries from Linux
-# Usage:
-#   cmake -S . -B build-win-mingw \
-#     -G Ninja \
-#     -DCMAKE_BUILD_TYPE=Release \
-#     -DCMAKE_TOOLCHAIN_FILE=cmake/toolchains/mingw-w64-x86_64.cmake
-
-set(CMAKE_SYSTEM_NAME Windows)
-set(CMAKE_SYSTEM_VERSION 10)
-
-# Adjust these prefixes if your distro uses different triplets
-set(TOOLCHAIN_PREFIX x86_64-w64-mingw32)
-
-find_program(CMAKE_C_COMPILER NAMES ${TOOLCHAIN_PREFIX}-gcc)
-find_program(CMAKE_CXX_COMPILER NAMES ${TOOLCHAIN_PREFIX}-g++)
-find_program(CMAKE_RC_COMPILER NAMES ${TOOLCHAIN_PREFIX}-windres)
-
-# For pkg-config in cross environment (optional)
-# set(ENV{PKG_CONFIG_LIBDIR} "")
-# set(ENV{PKG_CONFIG_PATH}   "")
-
-set(CMAKE_FIND_ROOT_PATH /usr/${TOOLCHAIN_PREFIX} /usr/${TOOLCHAIN_PREFIX}/${TOOLCHAIN_PREFIX})
-
-set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
-set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
-set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
-set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)