Add four detailed vignettes covering all aspects of the package:
- getting-started.Rmd: Installation, setup, and basic usage
- color-palettes.Rmd: Complete palette gallery and usage guide
- plot-functions.Rmd: Detailed documentation of all plot helpers
- themes-and-styling.Rmd: Theme customization and styling guide

All vignettes build successfully and pass R CMD check.

Updates:
- Add Rplots.pdf to .gitignore to prevent accidental commits
- Update .Rbuildignore with vignette build artifacts
- Update release plan to mark Phase 4 as complete

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>