Add Copilot instructions

Author: lukasmatta

.github/copilot-instructions.md

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+You are an expert in TypeScript, Angular, and scalable web application development. You write functional, maintainable, performant, and accessible code following Angular and TypeScript best practices.
+
+## TypeScript Best Practices
+
+- Use strict type checking
+- Prefer type inference when the type is obvious
+- Avoid the `any` type; use `unknown` when type is uncertain
+
+## Angular Best Practices
+
+- Always use standalone components over NgModules
+- Must NOT set `standalone: true` inside Angular decorators. It's the default in Angular v20+.
+- Use signals for state management
+- Implement lazy loading for feature routes
+- Do NOT use the `@HostBinding` and `@HostListener` decorators. Put host bindings inside the `host` object of the `@Component` or `@Directive` decorator instead
+- Use `NgOptimizedImage` for all static images.
+  - `NgOptimizedImage` does not work for inline base64 images.
+
+## Accessibility Requirements
+
+- It MUST pass all AXE checks.
+- It MUST follow all WCAG AA minimums, including focus management, color contrast, and ARIA attributes.
+
+### Components
+
+- Keep components small and focused on a single responsibility
+- Use `input()` and `output()` functions instead of decorators
+- Use `computed()` for derived state
+- Set `changeDetection: ChangeDetectionStrategy.OnPush` in `@Component` decorator
+- Prefer inline templates for small components
+- Prefer Reactive forms instead of Template-driven ones
+- Do NOT use `ngClass`, use `class` bindings instead
+- Do NOT use `ngStyle`, use `style` bindings instead
+- When using external templates/styles, use paths relative to the component TS file.
+
+## State Management
+
+- Use signals for local component state
+- Use `computed()` for derived state
+- Keep state transformations pure and predictable
+- Do NOT use `mutate` on signals, use `update` or `set` instead
+
+## Templates
+
+- Keep templates simple and avoid complex logic
+- Use native control flow (`@if`, `@for`, `@switch`) instead of `*ngIf`, `*ngFor`, `*ngSwitch`
+- Use the async pipe to handle observables
+- Do not assume globals like (`new Date()`) are available.
+- Do not write arrow functions in templates (they are not supported).
+
+## Services
+
+- Design services around a single responsibility
+- Use the `providedIn: 'root'` option for singleton services
+- Use the `inject()` function instead of constructor injection