fix(plugins): retry claude plugin install|update without -y on an old CLI

An older Claude Code has no -y on `plugin install|update` and exits with
"error: unknown option '-y'", so the dashboard's Update now chain failed at
its plugin_update step (and so did Update all, the plugin buttons and the
superpowers auto-install). Those versions also predate the confirmation
prompt -y answers, so every wrapper now retries the same argv without it
when, and only when, the CLI rejects the flag. /agenthub-update, which the
failure message points users to, falls back the same way.

server/lib/skill-plugins.js

@@ -128,6 +128,18 @@ function missingSkillPlugins() {
  * @returns {{ok: boolean, output: string}}
  */
 function runClaudePlugin(args, timeoutMs) {
+  const result = runClaudePluginOnce(args, timeoutMs);
+  // An older Claude Code rejects `-y` and never prompts; retry without it.
+  if (!result.ok && args.includes("-y") && /unknown option '-y'/.test(result.output)) {
+    return runClaudePluginOnce(
+      args.filter((a) => a !== "-y"),
+      timeoutMs
+    );
+  }
+  return result;
+}
+
+function runClaudePluginOnce(args, timeoutMs) {
   const env = { ...process.env };
   if (process.env.CLAUDE_HOME) env.CLAUDE_CONFIG_DIR = getClaudeHome();
   const result = spawnSync("claude", args, {