chore: v1.40.0.0 — gbrain sync hardening wave

Bumps VERSION 1.39.2.0 → 1.40.0.0 (MINOR — substantial gbrain capability
hardening across sync pipeline, install path, federation allowlist;
~600 net LOC added across 8 community PRs + plan-review refinements).

CHANGELOG entry follows the release-summary format: two-line headline,
lead paragraph, "numbers that matter" with before/after table across 8
user-visible surfaces, "what this means for builders" closer, itemized
Added/Changed/Fixed/NOT fixed/For contributors sections.

Per-commit contributor credits: 0xDevNinja, drummerms, Jayesh Betala,
Jason Shultz, genisis0x. Also names NikhileshNanduri and realcarsonterry
in the wave's "Fixed" section for independent submissions of the
.gbrain-source gitignore bug.

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "gstack",
-  "version": "1.39.2.0",
+  "version": "1.40.0.0",
   "description": "Garry's Stack — Claude Code skills + fast headless browser. One repo, one install, entire AI engineering workflow.",
   "license": "MIT",
   "type": "module",