fix: align all version manifests to 4.8.1 + guard against drift (#260, #262) (#270)

* fix: align all version manifests to 4.8.0 + guard against drift (#260, #262)

The v4.8.0 release shipped with all four plugin manifests still reading
4.7.0, and both package.json files still at the 0.1.0 npm-init default.
So Claude/Codex/Gemini reported 4.7.0 as the latest version (#262) and
the project advertised three different versions at once (#260).

Bump all six version-bearing files to 4.8.0 so they match the release tag:
the four plugin manifests, the root package.json, and ponytail-mcp.

Add scripts/check-versions.js, wired into CI, so this cannot recur. It
asserts every version file shares one pinned X.Y.Z version, and on a
release-tag run that the shared version equals the tag. The existing
mutual-agreement check in tests/gemini-extension.test.js could not catch
this, because all four manifests were stale at 4.7.0 together.

Fixes #260
Refs #262

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* fix: target 4.8.1 for a clean superseding release

v4.8.0 was already tagged with the stale 4.7.0 manifests. Rather than rewrite a published tag, ship the consistent versions as v4.8.1. The CI guard enforces tag == version on the release run. (#260, #262)

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

.github/plugin/plugin.json

@@ -1,7 +1,7 @@
 {
   "name": "ponytail",
   "description": "Lazy senior dev mode. Forces the simplest, shortest solution that actually works: YAGNI, stdlib first, no unrequested abstractions.",
-  "version": "4.7.0",
+  "version": "4.8.1",
   "author": {
     "name": "Dietrich Gebert",
     "url": "https://github.com/DietrichGebert"