feat(terra): replace tuigreet with a quickshell greeter

greetd now runs a throwaway Hyprland hosting dotfiles/quickshell/greeter.qml,
configured per host via homelab.greeter.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

dotfiles/quickshell/tests/LoginPanelHeadless.qml

@@ -0,0 +1,21 @@
+import QtQuick
+import qs.HyprChrome.Widgets.Greeter
+
+// Offscreen render of the login panel after a rejected password.
+//
+//   ./tools/quickshell-preview/render.sh \
+//     tests/LoginPanelHeadless.qml \
+//     .artifacts/quickshell-preview/login-panel.png 700 340
+LoginContent {
+    width: 640
+
+    hostName: "terra"
+    sessionName: "hyprland"
+    now: new Date(2026, 8, 18, 21, 47, 38)
+    user: "darman"
+    response: "hunter2"
+
+    message: "Authentication failure"
+    messageIsError: true
+    failed: true
+}