terra: migrate quickshell config into repo, add quickshell + opencode packages

Config was symlinked from ~/.dots/quickshell (separate dotfiles repo); now
tracked here and applied via home-manager xdg.configFile.

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

dotfiles/quickshell/shell.qml

@@ -0,0 +1,28 @@
+//@ pragma UseQApplication
+
+import Quickshell
+import qs.widgets.bar
+import qs.widgets.launcher
+import qs.widgets.notifications
+import qs.widgets.osd
+import qs.widgets.sidebar
+import qs.widgets.systray
+
+Scope {
+    // Left sidebar in the Slant (V6) style — toggle with SUPER CTRL S.
+    SideBar {}
+    BarBottom {}
+
+    // App launcher variants — toggled via Hyprland global shortcuts
+    // (SUPER CTRL 1/2/3). Try each and keep the one you like.
+    LauncherStack {}      // 1 — left vertical list
+    LauncherGrid {}       // 2 — centered icon grid
+    LauncherSpotlight {}  // 3 — top-center command bar
+    LauncherConsole {}    // 4 — full-width deck unfolding from the top bar
+    LauncherDock {}       // 5 — deck rising from the bottom bar
+    LauncherSlant {}      // 6 — angular / sheared panel
+    LauncherCorner {}     // 7 — Slant (V6) copy + floating power panel (shutdown/reboot)
+
+    Notifications {}
+    VolumeOsd {}
+}