tanin-greet: install greetd config via .install scriptlet (avoid file conflict)

greetd owns /etc/greetd/config.toml, so ship our config to
/usr/share/tanin/greetd/ and activate it from a post_install/post_upgrade
scriptlet (with a one-time backup). Fixes the pacman file conflict.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packaging/tanin-greet/tanin-greet.install

@@ -0,0 +1,24 @@
+# Activate the tanin-greet greetd config. greetd owns /etc/greetd/config.toml,
+# so we can't package that path — install it from the shipped template here,
+# backing up any existing (e.g. distro default / regreet) config once.
+_activate() {
+  local src=/usr/share/tanin/greetd/config.toml
+  local dst=/etc/greetd/config.toml
+  [ -f "$src" ] || return 0
+  if [ -e "$dst" ] && ! grep -q 'tanin-greet' "$dst" 2>/dev/null && [ ! -e "$dst.tanin-bak" ]; then
+    cp -a "$dst" "$dst.tanin-bak"
+  fi
+  install -Dm644 "$src" "$dst"
+}
+
+post_install() {
+  _activate
+  cat <<'EOF'
+>> tanin-greet: greetd now launches the TANINUX greeter (backup: /etc/greetd/config.toml.tanin-bak)
+   Enable the login screen with:  systemctl enable greetd   (disable any other DM first)
+EOF
+}
+
+post_upgrade() {
+  _activate
+}