Add GitHub Copilot instructions file for automated code review

.github/copilot-instructions.md

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+# Copilot Instructions for heatmaply
+
+This repository contains the `heatmaply` R package - an interactive cluster heatmap library built on top of `plotly` and `ggplot2`.
+
+## Repository Overview
+
+- **Type**: R Package
+- **Purpose**: Create interactive cluster heatmaps that can be saved as standalone HTML files, embedded in R Markdown documents, or displayed in Shiny apps
+- **Main dependencies**: plotly, ggplot2, dendextend, viridis
+
+## Code Review Guidelines
+
+When reviewing code changes in this repository, please consider:
+
+### R Code Standards
+
+- Follow R package development best practices (using `roxygen2` for documentation)
+- Ensure all exported functions have proper documentation with `@param`, `@return`, `@examples` tags
+- Use consistent naming conventions (snake_case for functions and variables)
+- Check for proper use of `@importFrom` and `@export` tags
+- Verify that examples are runnable and don't produce errors
+
+### Package-Specific Considerations
+
+- Changes to visualization functions should maintain backward compatibility with existing user code
+- New parameters should have sensible defaults
+- Consider performance implications when working with large matrices
+- Ensure changes work with both ggplot2 and plotly backends
+
+### Testing
+
+- Tests are located in the `tests/` directory using the `testthat` framework
+- New functionality should include appropriate test coverage
+- Verify that existing tests pass after changes
+
+### Documentation
+
+- Update `NEWS.md` for user-facing changes
+- Keep README.md examples up to date
+- Vignettes in `vignettes/` should reflect current API
+
+## Files to Pay Attention To
+
+- `R/heatmaply.R` - Main heatmap functions
+- `R/heatmapr.R` - Heatmap data preprocessing
+- `R/ggheatmap.R` - ggplot2-based rendering
+- `DESCRIPTION` - Package metadata and dependencies
+- `NAMESPACE` - Exported functions