Replace swaylock with gtklock; centralise theme palette

- Replace swaylock with gtklock (username + password form lockscreen)
- Add gtklock/config.ini and gtklock/style.css (Tomorrow Night theme)
- Update niri keybindings and swayidle to invoke gtklock -d
- Update packages.txt: swaylock -> gtklock
- Update install.sh: add AUR helper detection (yay/paru), symlink gtklock configs
- Add theme/colors.css (CSS custom properties) and theme/colors.json
- Update waybar/style.css, wofi/style.css, gtklock/style.css to import shared palette
- Update README.md with project summary and component table
- Add ARCHITECTURE.md and CLAUDE.md

niri/config.kdl

@@ -36,7 +36,7 @@ spawn-at-startup "mako"
 spawn-at-startup "swww-daemon"
 spawn-at-startup "nm-applet" "--indicator"
 spawn-at-startup "polkit-gnome-authentication-agent-1"
-spawn-at-startup "swayidle" "-w" "timeout" "300" "niri msg action power-off-monitors" "timeout" "600" "swaylock" "timeout" "1800" "systemctl suspend" "before-sleep" "swaylock"
+spawn-at-startup "swayidle" "-w" "timeout" "300" "niri msg action power-off-monitors" "timeout" "600" "gtklock" "-d" "timeout" "1800" "systemctl suspend" "before-sleep" "gtklock" "-d"
 spawn-at-startup "wl-paste" "--watch" "cliphist" "store"
 spawn-at-startup "blueman-applet"
 spawn-at-startup "wlsunset" "-l" "49.2" "-L" "-123.1"
@@ -88,7 +88,7 @@ binds {
     Mod+M { move-window-to-workspace "minimized"; }
     Mod+Shift+M { focus-workspace "minimized"; }
 
-    Mod+Shift+E { spawn "swaylock"; }
+    Mod+Shift+E { spawn "gtklock" "-d"; }
     Mod+Shift+P { spawn "powermenu"; }
     Mod+Shift+C { spawn "clipboard-picker"; }
     Mod+Shift+X { quit; }