Add category and publisher filtering to the game list

Closes #8

Description

Adds filtering controls to the game list page so users can narrow results by category and/or publisher. The game catalog's existing data model already includes categories and publishers, so this builds on existing structures without schema changes.

Related Issue

Closes #8 — Allow users to filter games by category and publisher

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to change)
• 📚 Documentation update
• 🧪 Test update
• 🔧 Refactor (no functional changes)

Changes Made

• Extended data-access helpers in src/lib/ to support filtering games by category and publisher
• Added support for combining category and publisher filters simultaneously
• Implemented accessible filter UI controls with data-testid attributes, ARIA labels, keyboard navigation, and visible focus states

Testing

Data Layer Changes

• Ran npm run test:unit - all tests pass
• Added/updated Vitest unit tests for filtering helpers
• Generated a migration (npm run db:generate) for any schema change

Frontend Changes

• Ran npm run test:e2e - all tests pass
• Added data-testid attributes to interactive elements
• Verified build succeeds (npm run build)

Checklist

• My code follows the project's coding standards
• I have used explicit TypeScript types for function parameters and return values
• I have built the UI with Astro components and Tailwind CSS utility classes (dark theme)
• I have updated documentation (README, instruction files) if needed
• My changes are focused on a single concern
• I have written clear commit messages explaining what and why

Additional Notes

This pairs naturally with the search feature in issue #2. Together, search and filtering would substantially improve how users discover games in the catalog.

Start by reading the existing data-access helpers in src/lib/ and the game list page to understand the current catalog flow and available categories and publishers. Run npm run test:unit and npm run test:e2e before making changes. Done means category and publisher filters work independently and together, with accessible controls, passing tests, and a successful npm run build.