chore: bump OpenClaw version to 2026.5.31

Bumps OpenClaw release metadata to 2026.5.31 across package manifests, app version files, plugin metadata, changelog headings, and generated shrinkwraps.

Verification:
- pnpm plugins:sync:check
- pnpm ios:version:check
- pnpm deps:shrinkwrap:check
- git diff --check
- stale 2026.5.30/build-code scan across changed files
- autoreview clean: no accepted/actionable findings
- PR CI green for real gates: Checks, security scans, dependency guard, app lanes, real behavior proof

Known non-code workflow issue:
- label workflow failed because this PR hits GitHub's 100-label issue cap before the size-label step.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "openclaw",
-  "version": "2026.5.30",
+  "version": "2026.5.31",
   "description": "Multi-channel AI gateway with extensible messaging integrations",
   "keywords": [],
   "homepage": "https://github.com/openclaw/openclaw#readme",