chore(security): pin Docker images by SHA digest

[williaby]

Summary

Pin Docker base images by SHA digest to fix OpenSSF Scorecard Pinned-Dependencies findings.

• python:3.12-slim -> @sha256:090ba77e2958f6af52a5341f788b50b032dd4ca28377d2893dcf1ecbdfdfe203 (all stages)
• ghcr.io/astral-sh/uv:latest -> ghcr.io/astral-sh/uv:0.11.16@sha256:440fd6477af86a2f1b38080c539f1672cd22acb1b1a47e321dba5158ab08864d
• node:22-alpine -> @sha256:968df39aedcea65eeb078fb336ed7191baf48f972b4479711397108be0966920 (3 stages in frontend/Dockerfile)
• nginx:alpine -> @sha256:8b1e78743a03dbb2c95171cc58639fef29abc8816598e27fb910ed2e621e589a (production stage in frontend/Dockerfile)

Why

Same root cause as ByronWilliamsCPA/llc-manager#51. Floating tags break supply-chain integrity; immutable digests make the build deterministic and the Scorecard score climb by ~1.0-1.5.

How the SHAs were resolved

• python:3.12-slim digest from Docker Hub tag API (last_updated 2026-05-22)
• uv digest from GHCR OCI registry manifest; the 0.11.16 version tag added alongside digest so Renovate can auto-bump
• node:22-alpine and nginx:alpine digests from Docker Hub tag API (last_updated 2026-05-14 and 2026-05-24 respectively)

Test plan

• CI passes (no functional change)
• Container security gate still satisfied
• Next Scorecard run shows Pinned-Dependencies score increase

Generated with Claude Code

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ℹ️ Review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 1bb81a7 and 8d4e525.

📒 Files selected for processing (2)

• Dockerfile
• frontend/Dockerfile

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch chore/sha-pin-docker-images

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[github-actions]

⚠️ Deprecation Warning: The deny-licenses option is deprecated for possible removal in the next major release. For more information, see issue 997.

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None

[Copilot]

Pull request overview

Pins Docker base images to immutable SHA256 digests to satisfy OpenSSF Scorecard “Pinned-Dependencies” findings and make container builds deterministic.

Changes:

• Pinned python:3.12-slim to a SHA digest in both builder and runtime stages of the backend Dockerfile.
• Pinned the uv tool image used for COPY --from=... to ghcr.io/astral-sh/uv:0.11.16@sha256:....
• Pinned node:22-alpine and nginx:alpine to SHA digests across all stages of frontend/Dockerfile.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
Dockerfile	Pins Python base image by digest and pins the uv image used for dependency tooling.
frontend/Dockerfile	Pins Node (deps/builder/dev) and Nginx (production) base images by digest.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud