docs(skills): add Overview and Red Flags sections (Phase 3)

[mcj-coder]

Summary

• Add standardized Overview sections to 16 skills that were missing them
• Add Red Flags - STOP sections with "Thought | Reality" tables to 21 skills
• Follows patterns from exemplar skills (issue-driven-delivery, skills-first-workflow)

Skills Updated

Added both Overview and Red Flags:

• dotnet-best-practices
• csharp-best-practices
• dotnet-bespoke-code-minimisation
• dotnet-domain-primitives
• dotnet-efcore-practices
• dotnet-mapping-standard
• dotnet-specification-pattern
• dotnet-testing-assertions
• dotnet-healthchecks
• dotnet-source-generation-first
• dotnet-open-source-first-governance
• innersource-governance-bootstrap
• observability-logging-baseline
• testing-strategy-dotnet

Added Overview only (already had Red Flags):

• component-boundary-ownership

Added Red Flags only (already had Overview):

• monorepo-orchestration-setup
• pair-programming
• safe-brownfield-refactor
• repo-best-practices-bootstrap
• security-processes
• testing-strategy-agnostic

Issues

• Refs: docs: Phase 3 - Structural Fixes #383
• Closes docs: Phase 3 - Structural Fixes #383

Test Plan

• npm run lint - All checks pass (CI workflow)
• All skills now have Overview and Red Flags sections (21 files changed)
• Red Flags follow "Thought | Reality" table pattern (commit ae89bda)

Verification

All 21 modified skill files pass lint checks.

Auto-merge

• Enable auto-merge after required approvals and checks pass

🤖 Generated with Claude Code

[github-actions]

	Warnings
⚠️	[Issue] 1 checked acceptance criteria may be missing evidence links. Recommended format: - [x] Item (evidence)
⚠️	[Issue] Plan found but no approval comment detected. Add approval comment (e.g., "Approval acknowledged" or "Plan approved") before implementation.

	Messages
📖	All PR validation checks passed.

Generated by 🚫 dangerJS against ae89bda

[martincjarvis]

LGTM - All 21 skills updated with consistent Overview and Red Flags sections following established patterns. All CI checks pass.