docs(readme): add primary language tag to game entries

[anupddas]

Summary

Closes #71.

Adds a **Language: X** tag to every game entry in README.md, inserted after the [[source]] link tag.

Why

Developers browsing this list often want to find games written in a specific language — to study idiomatic patterns, pick contribution targets, or evaluate a language for a new project. Without this metadata, every entry requires a click-through to the source repo.

Format used

Before:

[Game Name] - Description. [[source]]
[Game Name] - Description. Engine: [X] [[source]]

After:

[Game Name] - Description. [[source]] Languages: []
[Game Name] - Description. Engine: [X] [[source]] Language: []

Testing

Since this is a documentation-only change, traditional unit tests don't apply.

Verification method

Each language was determined by:

1. Checking the GitHub repo's top-level language badge.
2. Cross-referencing with the repo's own README where the language is stated explicitly.
3. For projects with multiple languages, the language of the game engine itself is used.

Checklist

• No existing links or engine tags broken
• Format consistent across all sections