chore: migrate coverage reporting from Codecov to Aikido

[Wikid82]

Summary

Replaces Codecov with the Aikido code-coverage action so Aikido PR checks receive the coverage report.

• Backend and agent Go coverage is converted to LCOV (gcov2lcov); frontend already emits LCOV.
• Each coverage job uploads its report as an artifact; one Upload Coverage to Aikido job combines them into a single upload per commit, as the action recommends.
• The action authenticates with GitHub OIDC (id-token: write on the upload job only); no repository secret is needed.
• The existing 85% coverage gates in scripts/*-coverage.sh are unchanged.
• Removed codecov.yml, the Codecov upload steps, the Codecov trigger-parity guard, and Codecov-specific helper prompts/examples. Docs updated.
• Workflow renamed to aikido-coverage.yml; nightly and weekly-promotion dispatches retargeted. Renovate trackers updated.

Notes for reviewers

• Job names changed (Backend Coverage, Frontend Coverage, Agent Coverage, Upload Coverage to Aikido). Update branch protection if it requires the old names or codecov/* statuses.
• The action defaults to the eu region; set region on the step if the workspace is elsewhere.
• The upload is skipped for fork and Dependabot PRs (no OIDC token).
• The real upload is untested until the first CI run; check the repository_source_paths log line and the Aikido UI.

Testing

actionlint and lefthook pre-commit pass locally; gcov2lcov output verified against existing coverage files.

Claude Code was used to help produce this change.

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[github-actions]

✅ Supply Chain Verification Results

✅ PASSED

📦 SBOM Summary

• Components: 1870

🔍 Vulnerability Scan

Severity	Count
🔴 Critical	0
🟠 High	0
🟡 Medium	0
🟢 Low	0
Total	0

📎 Artifacts

• SBOM (CycloneDX JSON) and Grype results available in workflow artifacts

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_{Generated by Supply Chain Verification workflow • View Details}