docs: close out secrets-filtering spec project

[zircote]

Summary

Archive the secrets-filtering spec project to docs/spec/completed/ with full retrospective.

Changes

• Move spec from active/ to completed/
• Add RETROSPECTIVE.md with completion metrics and learnings
• Update CLAUDE.md with completed project entry
• Update README.md status to completed
• Update CHANGELOG.md with final deliverables summary

Completion Metrics

Metric	Value
Outcome	Success
Effort	12 hours (within 8-16h estimate)
Test Coverage	87%+ (above 80% target)
Scope Variance	0%

Key Learnings Captured

• Code review (/cr + /cr-fx) caught 15+ issues
• Progressive 4-phase approach worked well
• Performance tests upfront prevented debates

[Copilot]

Pull request overview

This PR archives the completed secrets-filtering specification project by moving it from active/ to completed/ and adding comprehensive retrospective documentation. The project successfully implemented secrets filtering and sensitive data protection features with detect-secrets integration, custom PII detection, and SOC2/GDPR-compliant audit logging.

• Moved specification from active to completed directory structure
• Added RETROSPECTIVE.md documenting completion metrics, learnings, and recommendations
• Updated project status metadata to reflect completion (status, outcome, effort metrics)

Reviewed changes

Copilot reviewed 4 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
docs/spec/completed/2025-12-25-secrets-filtering/RETROSPECTIVE.md	New retrospective document with completion summary, learnings, and recommendations for future projects
docs/spec/completed/2025-12-25-secrets-filtering/REQUIREMENTS.md	Product requirements document moved to completed directory (14 P0, 6 P1, 5 P2 requirements)
docs/spec/completed/2025-12-25-secrets-filtering/README.md	Updated status to "completed" and added completion metadata (final_effort, outcome)
docs/spec/completed/2025-12-25-secrets-filtering/PROGRESS.md	Implementation progress tracking document moved to completed directory
docs/spec/completed/2025-12-25-secrets-filtering/IMPLEMENTATION_PLAN.md	Phased implementation plan (5 phases, 30 tasks) moved to completed directory
docs/spec/completed/2025-12-25-secrets-filtering/DECISIONS.md	Architecture Decision Records (12 ADRs) moved to completed directory
docs/spec/completed/2025-12-25-secrets-filtering/CHANGELOG.md	Added completion entry with deliverables summary and retrospective highlights
docs/spec/completed/2025-12-25-secrets-filtering/ARCHITECTURE.md	Technical architecture and design document moved to completed directory
CLAUDE.md	Added entry for completed secrets-filtering project with features and deliverables summary

Comments suppressed due to low confidence (1)

docs/spec/completed/2025-12-25-secrets-filtering/README.md:11

• The timeline is inconsistent: the project is marked as completed on 2025-12-25 but was approved on 2025-12-26T00:50:22Z (the next day). A project cannot be completed before it is approved. Either the completed date should be updated to 2025-12-26 or later, or the approved date should be earlier than 2025-12-25. Consider also adding a started field to track implementation timeline, as seen in other completed projects like fix-git-notes-fetch-refspec.