Add Opencode and Ollama modules; update configs

Enable Opencode and Ollama in home modules and import their Nix files.
Disable the deprecated system‑module opencode entries and remove it from
the
core packages list.
Add a new GitHub CLI module and a convenient `upf-gh` alias for flake
updates using a GitHub token.
Update the `stylix` configuration to include Opencode styling.
Refresh several flake.lock entries with newer revisions and hashes.

modules/home/gh.nix

@@ -0,0 +1,21 @@
+{
+  pkgs,
+  gitUsername,
+  ...
+}: {
+  programs.gh = {
+    enable = true;
+    package = pkgs.gh;
+    hosts."github.com" = {
+      git_protocol = "https";
+      users = [
+        "${gitUsername}"
+      ];
+      user = "${gitUsername}";
+    };
+    settings = {
+      git_protocol = "https";
+      version = "1";
+    };
+  };
+}