chore: replace Dependabot references with Renovate

- SECURITY.md: update to mention Renovate (org-wide Mend Renovate)
- PROJECT_ASSESSMENT.md: mark Renovate as integrated (org-wide config)

Closes PRI-389. Parent PRI-387.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

PROJECT_ASSESSMENT.md

@@ -229,7 +229,7 @@ Headlamp v0.39.0 with default `watchPlugins: true` treats catalog-managed plugin
 **Action Items:**
 - [ ] Parallelize test execution
 - [ ] Add npm cache to GitHub Actions
-- [ ] Integrate Dependabot
+- [x] Renovate is configured org-wide via `github>privilegedescalation/.github:renovate-config`
 - [ ] Add semantic-release
 
 ---

SECURITY.md

@@ -212,7 +212,7 @@ If you discover a security vulnerability in this plugin, please report it via:
 
 The project uses:
 - **npm audit**: Runs automatically during `npm install`
-- **Dependabot**: GitHub Dependabot monitors dependencies and creates PRs for updates
+- **Renovate**: Automated dependency updates via Mend Renovate (org-wide configured)
 - **GitHub Actions**: CI workflow runs `npm audit` on every commit
 
 ### Updating Dependencies