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, 23 insertions, 0 deletions

diff --git a/legacy-cpp/scripts/install_deps_alpine.sh b/legacy-cpp/scripts/install_deps_alpine.sh
new file mode 100644
index 0000000..2ebf131
--- /dev/null
+++ b/legacy-cpp/scripts/install_deps_alpine.sh
@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+if ! command -v apk >/dev/null 2>&1; then
+  echo "This script is intended for Alpine Linux (apk not found)." >&2
+  exit 1
+fi
+
+sudo apk update
+sudo apk add --no-cache \
+  build-base cmake ninja git pkgconf \
+  lua5.4 lua5.4-dev \
+  libx11-dev libxrandr-dev libxinerama-dev libxfixes-dev libxcursor-dev \
+  libxcb-dev xcb-util-keysyms-dev xcb-util-wm-dev \
+  libxft-dev \
+  wayland-dev wayland-protocols \
+  libxkbcommon-dev seatd-dev \
+  libdrm-dev mesa-egl mesa-gbm \
+  libinput-dev \
+  pixman-dev \
+  wlroots-dev || true
+
+echo "Dependencies installed."