terra: flatpak, unstable packages, GTK dark theme, comms workspace

- nix-flatpak input; discord, telegram, qbz as Flathub flatpaks; removes
  qbz and proton-pass-cli flake inputs
- proton-pass-cli and claude-code from nixpkgs-unstable via extraSpecialArgs
- dconf color-scheme = prefer-dark replaces per-session gsettings call

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

hosts/terra/home/hyprland.nix

@@ -257,7 +257,6 @@ in
           (lua ''
             function()
               hl.exec_cmd("systemctl --user start hyprpolkitagent")
-              hl.exec_cmd("gsettings set org.gnome.desktop.interface color-scheme 'prefer-dark'")
               hl.exec_cmd("vicinae server")
               hl.exec_cmd("quickshell")
               hl.exec_cmd("alacritty", { workspace = "special:terminal silent" })