release: v0.9.0 pre-release — X11 PAM integration, shadow suppression, macOS cfg guards

- PAM module now correctly fires on failed attempts (must precede auth includes)
- ahfail-display: sprite-sized window replaces full-screen overlay
- ahfail-display: XGrabKeyboard unlock detection replaces process scanning
- ahfail-display: _COMPTON_SHADOW=0 suppresses picom shadow without config changes
- ahfail-display: flock single-instance guard prevents stacking on rapid failures
- X11-specific code guarded behind #[cfg(target_os = "linux")] for macOS builds
- Removed debug logging (dlog/plog) from display and PAM binaries
- README: PAM ordering requirement, supported locker table, roadmap section

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Cargo.lock

@@ -13,6 +13,7 @@ name = "ahfail-display"
 version = "0.1.0"
 dependencies = [
  "ahfail-ui",
+ "cairo-rs",
  "cc",
  "gdk",
  "glib",