Add demo-04: signature list generator with code cleanup task

demo-04/README.md

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+# Demo 04: Signature List Generator - Code Cleanup
+
+## Purpose
+
+This is a static web application that turns student lists exported from UNIGRAZonline / CAMPUSonline (as "CSV for Excel") into nicely formatted signature lists for checking attendance. Everything happens locally in the browser - no sensitive data is transmitted anywhere.
+
+**Features:**
+- Upload CSV student lists exported from UNIGRAZonline
+- Filter by group name (manually entered or extracted from file)
+- Customizable course name and date
+- Include/exclude Uni Graz logo
+- Print-ready signature lists
+- Privacy-first: all processing happens client-side
+
+## Technology Stack
+
+- **Frontend:** Pure HTML5, CSS3, and vanilla JavaScript
+- **Styling:** Bootstrap 5.0.2 (via CDN)
+- **CSV Parsing:** PapaParse 5.4.1 (via CDN)
+- **Fonts:** Nunito Sans (Uni Graz corporate font)
+
+## Task: Code Cleanup
+
+This codebase needs cleanup and modernization. Your goal is to iteratively improve the codebase by:
+
+1. **Fixing bugs and issues** (syntax errors, missing semicolons, etc.)
+2. **Modernizing JavaScript** (replace `var` with `const`/`let`, use modern patterns)
+3. **Adding error handling** (invalid CSV, missing columns, edge cases)
+4. **Improving accessibility** (ARIA labels, keyboard navigation)
+5. **Code quality improvements** (consistent styling, remove duplication, better structure)
+
+## Process
+
+Work with the agent to identify issues and iteratively improve the code. For each change:
+- Explain what you're fixing and why
+- Get the agent's approval before making changes
+- Test the changes to ensure nothing breaks
+- Document your changes in a CHANGES.md file
+
+## Files
+
+- `index.html` - Main HTML structure
+- `main.css` - Styling and print styles
+- `main.js` - Application logic
+- `logo.png` - Uni Graz logo
+
+## Deployment
+
+This is a static site - simply upload all files to a web server. No build process or backend required.