feat(security): add OpenSSF Scorecard workflow and maximize score (#498)

* feat(security): add OpenSSF Scorecard workflow and maximize score

- Add scorecard.yml workflow (weekly + push to main) with SARIF upload
- Add CONTRIBUTING.md for contributor guidelines
- Add SLSA provenance attestation job to release workflow
- Add CycloneDX SBOM generation job to release workflow
- Pin Dockerfile base images to sha256 digests
- Enable Renovate pinDigests and platformAutomerge
- Add OpenSSF Scorecard badge to README

* fix(docs): address PR #498 review comments and remove .coderabbit.yaml

- Delete .coderabbit.yaml (falls back to shared org-level config)
- Add missing linter deps to CONTRIBUTING.md install step
- Separate make all and make test into distinct steps
- Fix line length note to match EditorConfig (200 chars, no MD override)
- Add yamllint/markdownlint to YAML/JSON/Markdown linter list
- Refine action references guidance
- Expand "Adding a New Action" section with action-docs and catalog info

.github/workflows/scorecard.yml

@@ -0,0 +1,37 @@
+---
+# yaml-language-server: $schema=https://json.schemastore.org/github-workflow.json
+name: OpenSSF Scorecard
+
+on:
+  push:
+    branches: [main]
+  schedule:
+    - cron: '0 2 * * 0' # Weekly Sunday 2AM UTC
+
+permissions: {}
+
+jobs:
+  analysis:
+    runs-on: ubuntu-latest
+    permissions:
+      security-events: write
+      id-token: write
+      contents: read
+      actions: read
+    steps:
+      - uses: actions/checkout@71cf2267d89c5cb81562390fa70a37fa40b1305e # v6-beta
+        with:
+          persist-credentials: false
+      - uses: ossf/scorecard-action@99c09fe975337306107572b4fdf4db224cf8e2f2 # v2.4.3
+        with:
+          results_file: results.sarif
+          results_format: sarif
+          publish_results: true
+      - uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
+        with:
+          name: SARIF file
+          path: results.sarif
+          retention-days: 5
+      - uses: github/codeql-action/upload-sarif@0d579ffd059c29b07949a3cce3983f0780820c98 # v4.32.6
+        with:
+          sarif_file: results.sarif