chore: add copilot instructions (#1872)

.github/copilot-instructions.md

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+# Nebula.js Development Guide for AI Agents
+
+## Project Overview
+
+Nebula.js is a framework for building and embedding Qlik visualizations. It's a **Lerna monorepo** managing multiple packages under `@nebula.js` npm scope. The core architecture separates visualization authoring (`supernova`) from rendering (`nucleus`) with `stardust` as the public API facade.
+
+## Architecture
+
+### Package Structure
+
+- **`apis/stardust/`** - Public API that exposes `nucleus` and `supernova` APIs. Entry point for consumers.
+- **`apis/nucleus/`** - React-based mashup runtime that renders visualizations in web apps
+- **`apis/supernova/`** - Hooks-based API for building custom visualizations (the "component" layer)
+- **`apis/locale/`** - Translation strings and locale generation (private)
+- **`apis/theme/`** - Theme access and consumption (private)
+- **`apis/conversion/`** - Conversion utilities for hyperCube extensions (private)
+- **`apis/enigma-mocker/`** - Mock enigma app for rendering without Qlik engine
+- **`apis/snapshooter/`** - Chart rendering as images
+- **`apis/test-utils/`** - Testing utilities
+- **`commands/`** - CLI tools (`build`, `serve`, `create`, `sense`) for visualization development
+- **`packages/ui/`** - Shared UI components (private)
+
+### Visualization Component Pattern (Supernova)
+
+Visualizations are defined as "supernovas" with this structure:
+
+```js
+export default function supernova(galaxy) {
+  return {
+    qae: {
+      properties: {},  // QIX object properties schema
+      data: {}        // Data definition (dimensions, measures)
+    },
+    component() {
+      // Hooks-based component using @nebula.js/stardust hooks
+      const element = useElement();
+      const layout = useLayout();
+      
+      useEffect(() => {
+        // Render logic here
+      }, [layout]);
+    }
+  };
+}
+```
+
+Key hooks from `@nebula.js/stardust`:
+- `useElement()` - Get the DOM element
+- `useLayout()` - Get QIX layout object  
+- `useModel()` - Access QIX model
+- `useStaleLayout()` - Layout that doesn't trigger re-renders
+- `useSelections()` - Handle user selections
+- `useConstraints()` - Interaction constraints (edit, select, active, passive)
+- `useEffect()`, `useState()`, etc. - React-like hooks
+
+See [apis/supernova/src/hooks.js](apis/supernova/src/hooks.js) for complete hook implementations.
+
+### Nucleus Rendering Flow
+
+Nucleus (React-based) orchestrates visualization rendering:
+1. `Supernova.jsx` component mounts the visualization element
+2. Calls supernova lifecycle: `created()` → `mounted()` → `render()` → `willUnmount()`
+3. Passes context (constraints, interactions, theme, appLayout) to component
+4. Uses `RenderDebouncer` to batch updates
+
+## Development Workflow
+
+### Setup & Build
+
+```bash
+yarn install                    # Install all dependencies
+yarn run locale:generate        # Generate translation files (required before build)
+yarn run build                  # Build all packages (production UMD + ESM)
+yarn run build:dev              # Build with source maps for development
+yarn run build:watch            # Watch mode for active development
+```
+
+**Critical**: Always run `locale:generate` before building if locale files changed.
+
+### Testing
+
+```bash
+yarn test:unit                  # Jest unit tests for all packages
+yarn test:component             # Playwright component tests
+yarn test:integration           # Playwright integration tests  
+yarn test:rendering             # Visual regression tests (Playwright)
+yarn test:mashup                # Full mashup integration tests
+```
+
+Unit tests use `jest` with `jest-environment-jsdom`. See [jest.config.js](jest.config.js) for coverage and test patterns.
+
+### CLI Commands for Visualizations
+
+When developing a supernova visualization:
+
+```bash
+nebula create <name>            # Scaffold new visualization
+nebula serve                    # Start dev server with hot reload
+nebula build                    # Build visualization for distribution
+nebula sense                    # Build as Qlik Sense extension
+```
+
+**Dev Server** (`nebula serve`):
+- Builds visualization to `/dist` automatically
+- Connects to Qlik Associative Engine (default: localhost:9076)
+- Supports fixtures for testing without engine connection
+- See [commands/serve/README.md](commands/serve/README.md) for options
+
+### Rollup Build Configuration
+
+All packages use shared [rollup.config.js](rollup.config.js):
+- **UMD format** for browsers (default export via `unpkg`/`jsdelivr`)
+- **ESM format** for bundlers (exposed via `module` field)
+- Creates `.dev.js` variants with source maps in development mode
+- Validates `main`, `module`, `unpkg`, `jsdelivr` targets in package.json match naming convention
+
+### Lerna Versioning
+
+This project uses Lerna for version management with **conventional commits**:
+- Use commit types: `feat:`, `fix:`, `chore:`, `docs:`, etc.
+- `lerna version` reads commits to determine semver bump
+- All packages are versioned together (see [lerna.json](lerna.json))
+
+## Code Conventions
+
+### ESLint Configuration
+
+- Uses **Airbnb style** with Prettier formatting
+- Flat config format ([eslint.config.mjs](eslint.config.mjs))
+- Jest environment globals enabled for test files
+- Custom rules: `max-len: 0`, `no-plusplus: 0`, React prop-types disabled
+
+### File Naming
+
+- Test files: `*.spec.js`, `*.test.js`, `*.spec.jsx`, `*.test.jsx`
+- Stories (Storybook): `**/__stories__/**`
+- Built artifacts: `dist/`, `lib/` (git-ignored)
+
+### Private Packages
+
+Packages like `locale`, `theme`, `conversion`, and `ui` are marked private/internal - they're consumed by stardust but not published as standalone packages.
+
+## Common Patterns
+
+### Picasso.js Integration
+
+Many visualizations use Picasso.js for rendering. Standard pattern:
+
+```js
+import picassojs from 'picasso.js';
+import picassoQ from 'picasso-plugin-q';
+
+const picasso = picassojs();
+picasso.use(picassoQ);
+
+// In component:
+const instance = picasso.chart({
+  element,
+  data: [{ type: 'q', key: 'qHyperCube', data: layout.qHyperCube }],
+  settings: definition({ layout })
+});
+```
+
+See [commands/create/templates/sn/picasso/common/src/index.js](commands/create/templates/sn/picasso/common/src/index.js).
+
+### Handling Selections
+
+Use `pic-selections` helper for Picasso-based charts to connect brush selections to QIX selections API. Example in templates.
+
+### Extension Points (`ext`)
+
+Qlik Sense extensions can define `ext` object for Sense-specific customizations (support.export, etc.). Pass `galaxy.anything.sense` to detect Sense environment.
+
+## Key Files to Reference
+
+- [apis/supernova/src/creator.js](apis/supernova/src/creator.js) - Component lifecycle implementation
+- [apis/nucleus/src/components/Supernova.jsx](apis/nucleus/src/components/Supernova.jsx) - React wrapper for visualizations
+- [apis/supernova/src/hooks.js](apis/supernova/src/hooks.js) - All available hooks
+- [.github/CONTRIBUTING.md](.github/CONTRIBUTING.md) - Contribution guidelines and git workflow
+
+## Debugging
+
+- **Build issues**: Check locale generation ran, verify package.json targets match rollup config expectations
+- **Hook errors**: "Invalid stardust hook call" means hooks called outside component function
+- **Visualization not updating**: Check if using `useStaleLayout()` vs `useLayout()` correctly - stale doesn't trigger re-renders