Show a catalog summary on the home page

The home page jumps straight into the featured games grid without giving visitors a sense of the catalog's size or quality. Adding a small summary — such as the total number of games and the average star rating — gives backers useful at-a-glance context and makes the landing page feel more alive. This builds entirely on data already available in the data layer.

Acceptance criteria

• The home page displays the total number of games in the catalog
• The home page displays the average star rating across games that have a rating
• The summary handles edge cases gracefully (no games, or no rated games)
• The summary follows the project's styling and accessibility guidelines and includes data-testid attributes
• A data-access helper computes the summary deterministically, with unit test coverage, and Playwright e2e tests verify it renders on the home page

Start at the home page entry point and trace the existing data layer for game and rating data. Add the catalog summary with the stated empty-state, styling, accessibility, and data-testid requirements, then add deterministic unit coverage for the data-access helper and Playwright e2e coverage confirming it renders on the home page.