feat(home): opencode module — link config/opencode → ~/.config/opencode

Adds metacfg.cli-apps.opencode (default enabled) which mounts the
in-repo opencode config (provider list, web-search skill) via
xdg.configFile, so all hosts pick it up automatically.

modules/home/cli-apps/opencode/default.nix

@@ -0,0 +1,23 @@
+{
+  lib,
+  config,
+  ...
+}:
+let
+  inherit (lib) mkIf;
+  inherit (lib.metacfg) mkBoolOpt;
+
+  cfg = config.metacfg.cli-apps.opencode;
+in
+{
+  options.metacfg.cli-apps.opencode = {
+    enable = mkBoolOpt true "Enable opencode config.";
+  };
+
+  config = mkIf cfg.enable {
+    xdg.configFile."opencode" = {
+      source = ../../../../config/opencode;
+      recursive = true;
+    };
+  };
+}