Disable Opencode; update flake.lock and librewolf

- Opencode module disabled in desktop, laptop, and default host configs
- Updated flake.lock revisions for firefox‑addons, home‑manager, nixpkgs
  and stylix
- Librewolf now uses pkgs.librewolf (source) instead of the binary
  package

hosts/Garand-Desktop/system-modules.nix

@@ -40,7 +40,7 @@ _: {
     */
     exercism.enable = true; # Exercism: coding practice platform
     lazygit.enable = false; # Lazygit: simple TUI for Git
-    opencode.enable = true; # OpenCode: tools for coding and development
+    opencode.enable = false; # OpenCode: tools for coding and development
     jan.enable = true; # Jan: AI chat UI
 
     /*