Add window rules, real config validation, and a Wayland DRM/udev backend

- srd.rule(): match windows by title/class, apply floating/maximized/
  workspace/geometry/decoration actions on creation (crates/core/src/rules.rs)
- srd.validate_config()/srd.debug.*: real range/format checks and
  status/profiling helpers, replacing the always-true stub
- Wayland titlebar text rendering via fontdue, unit-tested without a
  display (crates/wayland/src/decoration.rs)
- Wayland precise keybinding matching, replacing the "any Super-held key"
  heuristic, sharing the keysym table with X11 (moved to
  crates/core/src/keysyms.rs)
- Wayland DRM/udev backend (crates/wayland/src/udev.rs): runs as the real
  compositor on a bare TTY via libseat/libinput/KMS, software rendering
  via Pixman + dumb buffers (no GBM/EGL required)
- srdwm_platform::detect() fix, found via VM testing: a bare TTY with no
  DISPLAY/WAYLAND_DISPLAY now correctly resolves to Wayland instead of an
  X11 backend that can never work there
- XWayland integration groundwork (crates/wayland/src/xwayland.rs): spawn,
  X11Wm, and full XwmHandler event routing into the same WindowManager/
  Space pipeline as native clients. Windows don't render yet - a real
  glamor-vs-software-renderer conflict in XWayland's own fallback path,
  root-caused via WAYLAND_DEBUG tracing and documented in
  docs/IMPLEMENTATION_STATUS.md rather than worked around blind.

All verified live in an isolated QEMU VM: X11 backend shows two
decorated, correctly-tiled xterms with real title text; the DRM/udev
Wayland backend opens the GPU, initializes input, and scans out a
rendered frame via KMS page-flip.

1 files changed, 12 insertions, 5 deletions

diff --git a/config/srd/rules.lua b/config/srd/rules.lua
index 576333a..9435f69 100644
--- a/config/srd/rules.lua
+++ b/config/srd/rules.lua
@@ -1,6 +1,13 @@
-- Window rules (match-by-title/class -> action).
+- Window rules (match-by-title/class -> action), applied once when a
+- matching window is first created.
 --
-- A dedicated `srd.rule(...)` API is not implemented yet - see
-- docs/IMPLEMENTATION_STATUS.md. For now, achieve the same effect from
-- srd.bind()'d keys or by reacting to srd.window.focused() in your own
-- functions. This file is intentionally a no-op placeholder.
+- srd.rule(matcher, actions)
+--   matcher: { title = "substring, case-insensitive", class = "exact app_id/WM_CLASS, case-insensitive" }
+--            at least one of title/class is required - an empty matcher matches nothing.
+--   actions: { floating = bool, maximized = bool, workspace = id,
+--              x = .., y = .., width = .., height = ..,
+--              decorated = bool, border_color = {r,g,b}, border_width = px }
+--
+- Examples:
+- srd.rule({ class = "pavucontrol" }, { floating = true })
+- srd.rule({ title = "picture-in-picture" }, { floating = true, width = 480, height = 270 })