chore: migrate from Trivy to Grype for vulnerability scanning

[JAORMX]

Summary

• Replace aquasecurity/trivy-action with anchore/scan-action (Grype) v7.3.2
• Rename trivy.yml to security-scan.yml
• Drop secret scanning (not supported by Grype)
• Update SARIF upload to reference Grype output

Test plan

• Verify Grype scan runs successfully in CI
• Check SARIF results appear in Security tab

🤖 Generated with Claude Code

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