feat: add uninstall scripts for X11 and macOS

scripts/uninstall-linux-x11.sh — strips ahfail from common PAM service
files and removes binaries (via ninja uninstall or known paths).

scripts/uninstall-macos.sh — strips ahfail from screensaverui/screensaver
and removes /usr/local/lib/ahfail/.

README: add Uninstall section covering all four cases (X11, Wayland,
Homebrew macOS, manual macOS).

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

readme.md

@@ -151,6 +151,43 @@ auth optional /usr/local/lib/ahfail/libahfail_pam.so
 
 ---
 
+## Uninstall
+
+### Linux — X11
+
+```bash
+bash scripts/uninstall-linux-x11.sh
+```
+
+Removes the `ahfail` line from common PAM service files (`/etc/pam.d/i3lock`, `xscreensaver`, `lightdm`, etc.) and removes the installed binaries. If `builddir` is present it uses `ninja uninstall`; otherwise it removes the known paths manually.
+
+### Linux — Wayland
+
+No PAM config was modified. Just stop passing the module to gtklock and optionally remove the file:
+
+```bash
+sudo rm -f /usr/lib/gtklock/ahfail-module.so   # --prefix=/usr install
+# or
+sudo rm -f /usr/local/lib/gtklock/ahfail-module.so
+```
+
+### macOS — Homebrew
+
+```bash
+sudo sed -i '' '/ahfail/d' /etc/pam.d/screensaverui   # or screensaver on macOS 12
+brew uninstall ahfail
+```
+
+### macOS — manual / script install
+
+```bash
+bash scripts/uninstall-macos.sh
+```
+
+Removes the `ahfail` line from the screensaver PAM file and deletes `/usr/local/lib/ahfail/`.
+
+---
+
 ## Customization
 
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