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

gtklock/config.ini

@@ -0,0 +1,4 @@
+[main]
+gtk-theme=Materia-dark
+style=/home/alex/.config/gtklock/style.css
+follow-focus=true

gtklock/style.css

@@ -0,0 +1,72 @@
+@import url("../theme/colors.css");
+
+/* gtklock style - Tomorrow Night theme */
+
+window {
+  background-color: var(--tn-bg);
+}
+
+#body {
+  background-color: transparent;
+}
+
+#clock-label {
+  color: var(--tn-fg);
+  font-family: "JetBrainsMono Nerd Font";
+  font-size: 48px;
+  font-weight: bold;
+  margin-bottom: 8px;
+}
+
+#date-label {
+  color: var(--tn-fg-dim);
+  font-family: "JetBrainsMono Nerd Font";
+  font-size: 16px;
+  margin-bottom: 24px;
+}
+
+#username-label {
+  color: var(--tn-fg);
+  font-family: "JetBrainsMono Nerd Font";
+  font-size: 18px;
+  font-weight: bold;
+  margin-bottom: 12px;
+}
+
+#input-box {
+  background-color: var(--tn-bg-alt);
+  border: 2px solid var(--tn-bg-high);
+  border-radius: 6px;
+  color: var(--tn-fg);
+  font-family: "JetBrainsMono Nerd Font";
+  font-size: 14px;
+  padding: 8px 12px;
+  min-width: 280px;
+}
+
+#input-box:focus {
+  border-color: var(--tn-blue);
+}
+
+#error-label {
+  color: var(--tn-red);
+  font-family: "JetBrainsMono Nerd Font";
+  font-size: 13px;
+  margin-top: 8px;
+}
+
+#unlock-button {
+  background-color: var(--tn-bg-high);
+  border: none;
+  border-radius: 6px;
+  color: var(--tn-fg);
+  font-family: "JetBrainsMono Nerd Font";
+  font-size: 14px;
+  padding: 8px 20px;
+  margin-top: 12px;
+}
+
+#unlock-button:hover {
+  background-color: var(--tn-blue);
+  color: var(--tn-bg);
+}