docs: add skills workflow guide with full 7-step development pipeline
Summary
- New /docs/workflow page covering all 7 skills in the development pipeline
- Each skill documented with purpose, inputs, outputs, and usage instructions
- Includes real-world example and document output overview
- Added to sidebar under User Guide section
Why
Users needed a single document that explains what each skill does, how they chain together, and what documents are produced at each step.
Changes
- New: src/app/docs/workflow/page.tsx
- Modified: src/components/docs/DocsSidebar.tsx