CONTRIBUTING lists two translated READMEs when the repository has four

## What

CONTRIBUTING names two translated READMEs. The repository has four, and the drift guard enforces all four. A contributor reading CONTRIBUTING would not know that a change to the engine list has to reach `README_es.md` and `README_ur.md` as well.

## Where

`CONTRIBUTING.md` line 13:

```
The exceptions are the translated READMEs themselves ([README_zh.md](README_zh.md), [README_ja.md](README_ja.md)), which are maintained in their own language.
```

and line 76:

```
6. **Localized READMEs are guarded.** `README_zh.md` and `README_ja.md` must list the same engines
```

The repository actually ships `README_es.md`, `README_ja.md`, `README_ur.md` and `README_zh.md`, and the drift check covers all four.

## Expected

Both places list all four translated READMEs, so the guard and the instructions agree.

## How to fix

1. In `CONTRIBUTING.md` line 13, add `README_es.md` and `README_ur.md` to the parenthesised list, keeping the same link format.
2. In `CONTRIBUTING.md` line 76, extend the sentence to name all four files.
3. Before you write the list, run `ls README_*.md` and use what it returns, so the text matches the tree rather than this issue.

## How to check

`ls README_*.md` and the two CONTRIBUTING passages should name the same set of files.

Start by running `ls README_*.md` to confirm the repository’s translated README set. Read the two noted passages in `CONTRIBUTING.md`, update their lists to match that command’s output, and verify that both passages name the same files.

Written by the indexing model from the issue text.