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/__tests__/cc-plugin-cli.test.js

@@ -116,6 +116,22 @@ describe("cc-plugin-cli argv construction", () => {
     }
   });
 
+  it("retries without -y on a Claude Code too old to know the flag", async () => {
+    // Older CLIs answer `error: unknown option '-y'` and exit 1; they also
+    // never prompt, so the same command without the flag is the right retry.
+    const restore = stubClaude(
+      'for a in "$@"; do [ "$a" = "-y" ] && { echo "error: unknown option \'-y\'" >&2; exit 1; }; done\n' +
+        'for a in "$@"; do echo "$a"; done'
+    );
+    try {
+      const r = await cli.pluginUpdate({ spec: "demo@m" });
+      assert.equal(r.ok, true);
+      assert.deepEqual(argvOf(r), ["plugin", "update", "demo@m"]);
+    } finally {
+      restore();
+    }
+  });
+
   it("passes -y on install so a non-TTY run never waits for a prompt", async () => {
     const restore = stubClaude();
     try {