Update styling and conventions for modern primer-react

.gitignore

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 # production
 /build
+/dist
 
 # misc
 .DS_Store

AGENTS.md

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+# Copilot Instructions
+
+## Build & Development
+
+```bash
+npm install          # Install dependencies
+npm run dev          # Start dev server at http://localhost:1234
+npm run build        # Production build
+npm run lint         # Run ESLint
+```
+
+## Architecture
+
+This is a **Primer React prototyping app** using Vite and file-based routing via `@generouted/react-router`.
+
+### Routing
+
+Routes are auto-generated from the file structure in `src/pages/`:
+- `src/pages/index.jsx` → `/`
+- `src/pages/Overview.jsx` → `/Overview`
+- `src/pages/Issues.jsx` → `/Issues`
+
+To create a new page, add a `.jsx` file to `src/pages/` and it will automatically be available at the corresponding URL path.
+
+### Component Organization
+
+- **`src/pages/`** - Route components (each file = one route)
+- **`src/components/`** - Reusable UI components (GlobalNavigation, SidebarNavigation, etc.)
+- **`src/templates/`** - Page layout templates (e.g., `Application` template with header + sidebar)
+
+### Layout Pattern
+
+Pages typically use the `Application` template which provides:
+- Global navigation header with customizable `topnav` items
+- Optional `sidenav` sidebar navigation
+- Main content area via `children`
+
+```jsx
+<Application title="Primer" subtitle="React" topnav={topnav} sidenav={sidenav}>
+  {/* Page content */}
+</Application>
+```
+
+## Key Conventions
+
+- Use **Primer React** components from `@primer/react` for all UI elements
+- Use **Primer Octicons** from `@primer/octicons-react` for icons
+- Use **CSS Modules** (`*.module.css`) for component-specific styles
+- Default theme is `night` mode with `dark_dimmed` scheme (configured in `src/index.jsx`)