security: harden CI against supply-chain attacks (#20476)

- Pin all third-party actions to SHA
- Gate claude.yml triggers to internal authors with Harden-Runner egress
audit
- Ignore fork-PR lifecycle scripts
- Narrow cross-repo dispatch payloads
- Add 7d npm release-age gate
- Add CODEOWNERS on .github/** and .yarnrc.yml

---------

Co-authored-by: prastoin <paul@twenty.com>

.cursor/rules/github-actions-security.mdc

@@ -0,0 +1,72 @@
+---
+description: GitHub Actions security guidelines for supply chain protection
+globs: **/.github/**/*.yml, **/.github/**/*.yaml
+alwaysApply: false
+---
+
+# GitHub Actions Security
+
+## Pin Third-Party Actions to Commit SHAs
+
+Always reference external actions and reusable workflows by their full commit SHA, never by a mutable tag or branch. Tags can be force-pushed by a compromised maintainer account.
+
+```yaml
+# ❌ Mutable tag — vulnerable to supply chain attacks
+uses: actions/checkout@v4
+uses: actions/setup-node@v4
+
+# ✅ Pinned to commit SHA with tag comment for readability
+uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.3.1
+uses: actions/setup-node@49933ea5288caeca8642d1e84afbd3f7d6820020 # v4.4.0
+```
+
+## Prefer `gh api` Over Third-Party Dispatch Actions
+
+For repository dispatch calls, use `gh api` directly instead of third-party actions like `peter-evans/repository-dispatch`. This eliminates a supply-chain dependency entirely.
+
+```yaml
+# ✅ Use env vars + bracket notation to prevent injection
+- name: Dispatch to target repo
+  env:
+    GH_TOKEN: ${{ secrets.DISPATCH_TOKEN }}
+    PR_NUMBER: ${{ github.event.pull_request.number }}
+    BRANCH: ${{ github.event.workflow_run.head_branch }}
+  run: |
+    gh api repos/org/repo/dispatches \
+      -f event_type=my-event \
+      -f "client_payload[pr_number]=$PR_NUMBER" \
+      -f "client_payload[branch]=$BRANCH"
+
+# ✅ Simple dispatch without payload
+- name: Trigger workflow
+  env:
+    GH_TOKEN: ${{ secrets.DISPATCH_TOKEN }}
+  run: |
+    gh api repos/org/repo/dispatches -f event_type=my-event
+
+# ❌ Third-party action dependency
+- uses: peter-evans/repository-dispatch@v2
+  with:
+    token: ${{ secrets.DISPATCH_TOKEN }}
+    repository: org/repo
+    event-type: my-event
+
+# ❌ Inline ${{ }} in shell — vulnerable to injection
+- run: |
+    gh api repos/org/repo/dispatches --input - <<EOF
+    {"event_type": "x", "client_payload": {"branch": "${{ github.head_ref }}"}}
+    EOF
+```
+
+## Minimal Permissions
+
+Always declare explicit `permissions` at the job level with the least privilege required. Never rely on the default `GITHUB_TOKEN` permissions.
+
+```yaml
+# ✅ Explicit minimal permissions
+permissions:
+  contents: read
+
+# ❌ Overly broad or implicit permissions
+permissions: write-all
+```