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>

hosts/terra/home.nix

@@ -57,10 +57,13 @@
   # indexes share/mime/packages inside the hm profile itself, so this has to
   # be a package in home.packages, not a plain xdg.dataFile.
   xdg.mime.enable = true;
+  xdg.configFile."quickshell".source = ../../dotfiles/quickshell;
   home.packages = [
     (pkgs.writeTextDir "share/mime/packages/application-x-ms-sln.xml"
       (builtins.readFile ../../dotfiles/mime/application-x-ms-sln.xml))
     pkgs.claude-code
+    pkgs.quickshell
+    pkgs.opencode
   ];
 
   programs.alacritty = {