Adding nightly and PR trivy scans

[jmfiola]

Automated Trivy Security Scans

This PR adds automated Trivy scans to every pull request targeting main and sets up a nightly job that runs the same scan directly against the main branch.

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 Key Changes

Workflow	Frequency	Behaviour
Pull Request	Every PR to main	Fails if any HIGH or CRITICAL vulnerabilities, or secrets are detected.
Nightly (main)	Daily ‑ 03:00 UTC	Runs on main; when the scan fails on HIGH or CRITICAL findings, the workflow opens  or re‑uses  a GitHub issue. Example: Issue #13.

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Type of Change

New feature – adds preventive security gates and continuous monitoring.

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Validation & Testing

Pull‑Request Pipeline

• Tested with branches containing known HIGH/CRITICAL findings → workflow failed as expected.
• Tested with a clean branch → workflow passed.

Nightly Workflow

• Temporarily removed branch/schedule guard to trigger issue‑creation logic.
• Confirmed:
  • A single issue is opened on first failure.
  • Subsequent failures detect the open issue and do not create duplicates.