Add comprehensive GitHub Copilot instructions for Fantasy Map Generator (#1233)

* Initial plan

* Add comprehensive GitHub Copilot instructions for Fantasy Map Generator

Co-authored-by: Azgaar <26469650+Azgaar@users.noreply.github.com>

* chore: copilot instructions

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Azgaar <26469650+Azgaar@users.noreply.github.com>
Co-authored-by: Azgaar <azgaar.fmg@yandex.com>

.github/copilot-instructions.md

@@ -0,0 +1,89 @@
+# Fantasy Map Generator
+
+Azgaar's Fantasy Map Generator is a client-side JavaScript web application for creating fantasy maps. It generates detailed fantasy worlds with countries, cities, rivers, biomes, and cultural elements.
+
+Always reference these instructions first and fallback to search or bash commands only when you encounter unexpected information that does not match the info here.
+
+## Working Effectively
+
+- **CRITICAL**: This is a static web application - NO build process needed. No npm install, no compilation, no bundling.
+- Run the application using HTTP server (required - cannot run with file:// protocol):
+  - `python3 -m http.server 8000` - takes 2-3 seconds to start
+- Access at: `http://localhost:8000`
+
+## Validation
+
+- Always manually validate any changes by:
+  1. Starting the HTTP server (NEVER CANCEL - wait for full startup)
+  2. Navigate to the application in browser
+  3. Click the "►" button to open the menu and generate a new map
+  4. **CRITICAL VALIDATION**: Verify the map generates with countries, cities, roads, and geographic features
+  5. Test UI interaction: click "Layers" button, verify layer controls work
+  6. Test regeneration: click "New Map!" button, verify new map generates correctly
+- **Known Issues**: Google Analytics and font loading errors are normal (blocked external resources)
+
+## Repository Structure
+
+### Core Files
+
+- `index.html` - Main application entry point
+- `main.js` - Core application logic
+- `versioning.js` - Version management and update handling
+
+### Key Directories
+
+- `modules/` - core functionality modules:
+  - `modules/ui/` - UI components (editors, tools, style management)
+  - `modules/dynamic/` - runtime modules (export, installation)
+  - `modules/renderers/` - drawing and rendering logic
+- `utils/` - utility libraries (math, arrays, strings, etc.)
+- `styles/` - visual style presets (JSON files)
+- `libs/` - Third-party libraries (D3.js, TinyMCE, etc.)
+- `images/` - backgrounds, UI elements
+- `charges/` - heraldic symbols and coat of arms elements
+- `config/` - Heightmap templates and configurations
+- `heightmaps/` - Terrain generation data
+
+## Common Tasks
+
+### Making Code Changes
+
+1. Edit JavaScript files directly (no compilation needed)
+2. Refresh browser to see changes immediately
+3. **ALWAYS test map generation** after making changes
+4. Update version in `versioning.js` for all changes
+5. Update file hashes in `index.html` for changed files (format: `file.js?v=1.108.1`)
+
+### Debugging Map Generation
+
+- Open browser developer tools console
+- Look for timing logs, e.g. "TOTAL: ~0.76s"
+- Map generation logs show each step (heightmap, rivers, states, etc.)
+- Error messages will indicate specific generation failures
+
+### Testing Different Map Types
+
+- Use "New Map!" button for quick regeneration
+- Access "Layers" menu to change map visualization
+- Available presets: Political, Cultural, Religions, Biomes, Heightmap, Physical, Military
+
+## Troubleshooting
+
+### Application Won't Load
+
+- Ensure using HTTP server (not file://)
+- Check console for JavaScript errors
+- Verify all files are present in repository
+
+### Map Generation Fails
+
+- Check browser console for error messages
+- Look for specific module failures in generation logs
+- Try refreshing page and generating new map
+
+### Performance Issues
+
+- Map generation should complete in ~1 second for standard configurations
+- If slower, check browser console for errors
+
+Remember: This is a sophisticated client-side application that generates complete fantasy worlds with political systems, geography, cultures, and detailed cartographic elements. Always validate that your changes preserve the core map generation functionality.