fix(release): stage the plugins/ecc Codex manifest when bumping

update_version rewrote plugins/ecc/.codex-plugin/plugin.json on disk, but
CODEX_MARKETPLACE_PLUGIN_JSON was missing from the git add list, so the bump
was never committed. The tag then carried a 2.0.0 manifest and
plugin-manifest.test.js failed the release in CI.

Also commits the 2.1.0 value the previous run left uncommitted.

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0149VwNuynam6rvEfcMmiHHa

plugins/ecc/.codex-plugin/plugin.json

@@ -1,6 +1,6 @@
 {
   "name": "ecc",
-  "version": "2.0.0",
+  "version": "2.1.0",
   "description": "Harness-native ECC workflows for Codex: shared skills, production-ready MCP configs, and selective-install-aligned conventions for TDD, security scanning, code review, and autonomous development.",
   "author": {
     "name": "Affaan Mustafa",