[IC-096] Add privacy-safe product metrics for completion, abandonment, review, latency, and failure reasons.

[github-actions]

Outcome

Add privacy-safe product metrics for completion, abandonment, review, latency, and failure reasons.

Acceptance checks

• Metrics have documented definitions; tenant access is isolated; small-cohort/PII leakage is prevented; opt-out/retention are defined.

Dependencies

IC-067, IC-087

Planning metadata

• Priority: P1
• Milestone: Milestone 9 — Operations and pilot readiness

Definition of done

• Automated tests cover the change where practical.
• Tenant/environment isolation and failure paths were reviewed.
• Logs and errors contain no secrets, PII, documents, or biometric data.
• Relevant API, architecture, operations, and user documentation is updated.
• The pull request links this issue and lists verification commands.
  Generated from docs/planning/implementation-backlog.md; edit the backlog and rerun the sync to change generated fields.