Add structured test-gap audit entries across regression, CLI, Docker, release, and reproducibility

[Copilot]

This issue asked for a coverage-gap audit that is actionable across testing priorities (regression, integration, CLI E2E, Docker, release/package, benchmark reproducibility, failure paths, and save/load image validation).
This PR adds a single consolidated audit section that defines each gap in a trackable issue format.

• What changed

  • Added ## Audit: Test Coverage Gap Issues to docs/PRODUCT_AUDIT.md.
  • Added 8 explicit gap entries, one per requested focus area.

• Issue format applied to every entry

  • Title
  • Missing test coverage area
  • Risk if not covered
  • Suggested test strategy
  • Acceptance criteria
  • Labels

• Why this is useful

  • Converts broad audit intent into implementation-ready backlog items with clear done criteria.
  • Standardizes triage metadata (labels) for prioritization and workflow routing.

Example of the added structure:

### 4) Docker workflow runtime validation
- **Missing test coverage area:** Docker assets exist, but tests do not validate container build/run workflows for application and benchmark images.
- **Risk if not covered:** Published images may build but fail at runtime due to dependency, entrypoint, or path-mapping issues.
- **Suggested test strategy:** Add CI job(s) to build both Dockerfiles and run smoke commands (`auralock --help`, benchmark preflight) in containers.
- **Acceptance criteria:** CI verifies image build + smoke execution for `Dockerfile` and `Dockerfile.benchmark`.
- **Labels:** `testing`, `docker`, `ci`

Original prompt

---

This section details on the original issue you should resolve

<issue_title>audit test gaps</issue_title>
<issue_description>
Focus on:

• regression gaps
• integration gaps
• CLI end-to-end coverage
• Docker workflow validation
• release/package verification
• benchmark reproducibility
• failure-path coverage
• image output validation after save/load

For each issue, include:

• Title
• Missing test coverage area
• Risk if not covered
• Suggested test strategy
• Acceptance criteria
• Labels
  </issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes audit test gaps #7

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