Add comprehensive CI workflows

[pdettori]

Summary

Phase 4 of repo orchestration — comprehensive CI for agent-toolkit.

• ci.yaml — Pre-commit hooks + lint + test (Python 3.11, uv, ruff, pytest)
• security-scans.yaml — Dependency review, Trivy filesystem scan (CRITICAL+HIGH → SARIF), CodeQL Python with security-extended queries, action SHA-pinning verification
• scorecard.yaml — OpenSSF Scorecard (weekly + on push to main, SARIF upload to Security tab)
• stale.yaml — Reusable kagenti org workflow for stale issues/PRs
• dependabot.yml — Weekly updates for pip and github-actions ecosystems

Supply chain hardening

• All actions SHA-pinned (no tag-only references)
• Explicit least-privilege permissions on every job
• timeout-minutes: 15 on CI jobs
• Trivy + CodeQL SARIF results uploaded to GitHub Security tab

Test plan

• Verify ci.yaml triggers on PR and runs pre-commit + lint successfully
• Verify security-scans.yaml runs dependency review, Trivy, CodeQL, and action-pinning check
• Verify scorecard.yaml runs on push to main
• Verify dependabot creates PRs for pip and github-actions updates

🤖 Generated with Claude Code

[github-advanced-security]

You are seeing this message because GitHub Code Scanning has recently been set up for this repository, or this pull request contains the workflow file for the Code Scanning tool.

What Enabling Code Scanning Means:

• The 'Security' tab will display more code scanning analysis results (e.g., for the default branch).
• Depending on your configuration and choice of analysis tool, future pull requests will be annotated with code scanning analysis results.
• You will be able to see the analysis results for the pull request's branch on this overview once the scans have completed and the checks have passed.

For more information about GitHub Code Scanning, check out the documentation.

[pdettori]

There is no python code to test and scan yet, so CI failures are expected