ci: run native OpenSpec and local link validation in verify (WealthLedger/specs#2)

npm run validate: toolchain check, openspec schema validate, openspec validate --all --strict, lychee --offline --include-fragments for root *.md and openspec/specs. CI verify installs the pinned CLI and sha256-pinned lychee and runs it.

Closes #2

package.json

@@ -8,6 +8,7 @@
   "scripts": {
     "verify": "git diff --check",
     "check:openspec": "node scripts/check-openspec.cjs",
+    "validate": "npm run check:openspec && openspec schema validate && openspec validate --all --strict --no-interactive --store wealth-ledger-specs && lychee --offline --include-fragments --no-progress './*.md' openspec/specs",
     "release:preview": "release-it --dry-run --ci",
     "release:prepare": "release-it --ci",
     "commitlint": "commitlint",