Invalid words (e.g. "ZZZZZ") are accepted as guesses

[copilot-swe-agent]

Summary

Guesses that are not real words (e.g. ZZZZZ) are accepted by the game as valid guesses, even though they should be rejected.

Root cause

In src/components/GuessForm/GuessForm.js, guess validation only checks that the input is 5 characters A-Z:

const validateLength = /([A-Z]){5}/g

if (!guess.match(validateLength)) {
  return window.alert("Guess must have exactly 5 A-Z characters")
}

There is no check anywhere in the codebase that the guess is an actual valid word. The WORDS list in src/data.js is only used to pick the secret answer (sample(WORDS) in Game.js) - it is never used to validate a submitted guess.

Reproduction

const validateLength = /([A-Z]){5}/g;
"ZZZZZ".match(validateLength); // truthy -> guess is accepted

Typing ZZZZZ (or any other 5 letter A-Z string) into the guess input and submitting it is accepted as a normal guess, consuming one of the player's attempts, even though ZZZZZ is not in the word list and isn't a real word.

Suggested fix

Validate the submitted guess against a word list (either reuse WORDS from src/data.js, or add a separate, larger dictionary of acceptable guesses) before accepting it, and show an alert like "Not in word list" if it doesn't match, similar to the real Wordle.