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, 36 insertions, 0 deletions

diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..40aa207
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,36 @@
+[workspace]
+resolver = "2"
+members = [
+    "crates/srdwm",
+    "crates/core",
+    "crates/config",
+    "crates/platform",
+    "crates/x11",
+    "crates/wayland",
+    "crates/windows",
+    "crates/macos",
+]
+
+[workspace.package]
+version = "0.1.0"
+edition = "2021"
+rust-version = "1.80"
+license = "MIT"
+authors = ["srdusr"]
+repository = "https://github.com/srdusr/srdwm"
+
+[workspace.dependencies]
+srdwm-core = { path = "crates/core" }
+srdwm-config = { path = "crates/config" }
+srdwm-platform = { path = "crates/platform" }
+srdwm-x11 = { path = "crates/x11" }
+srdwm-wayland = { path = "crates/wayland" }
+srdwm-windows = { path = "crates/windows" }
+srdwm-macos = { path = "crates/macos" }
+
+log = "0.4"
+env_logger = "0.11"
+thiserror = "2"
+
+[profile.release]
+lto = "thin"