chore(release): bump to v1.4.0.0 + CHANGELOG entry for prompt injection guard

After merging origin/main (which brought v1.3.0.0), this branch needs
its own version bump per CLAUDE.md: "Merging main does NOT mean adopting
main's version. If main is at v1.3.0.0 and your branch adds features,
bump to v1.4.0.0 with a new entry. Never jam your changes into an entry
that already landed on main."

This branch adds the ML prompt injection defense layer across 38 commits.
Minor bump (.3 -> .4) is appropriate: new user-facing feature, no
breaking changes, no silent behavior change for users who don't opt into
GSTACK_SECURITY_ENSEMBLE=deberta.

VERSION + package.json synced. CHANGELOG entry reads user-first per
CLAUDE.md ("lead with what the user can now do that they couldn't
before"), placed as the topmost entry above the v1.3 release notes
that came in via the merge.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "gstack",
-  "version": "1.3.0.0",
+  "version": "1.4.0.0",
   "description": "Garry's Stack — Claude Code skills + fast headless browser. One repo, one install, entire AI engineering workflow.",
   "license": "MIT",
   "type": "module",