impr(input-history): Change style for incomplete last word in input history (@Leonabcd123) (#7117)

### Description

Added a new style named "incomplete" that mirrors the error style, but
uses yellow for the color. Words are marked in this style when they
don't match the correct word exactly, but share the same prefix.

Implements #6690

---------

Co-authored-by: Jack <[email protected]>

Author: Leonabcd123

frontend/src/ts/test/test-ui.ts

@@ -1286,7 +1286,8 @@ function buildWordLettersHTML(
 async function loadWordsHistory(): Promise<boolean> {
   $("#resultWordsHistory .words").empty();
   let wordsHTML = "";
-  for (let i = 0; i < TestInput.input.getHistory().length + 2; i++) {
+  const inputHistoryLength = TestInput.input.getHistory().length;
+  for (let i = 0; i < inputHistoryLength + 2; i++) {
     const input = TestInput.input.getHistory(i);
     const corrected = TestInput.corrected.getHistory(i);
     const word = TestWords.words.get(i);
@@ -1303,8 +1304,19 @@ async function loadWordsHistory(): Promise<boolean> {
         throw new Error("empty input word");
       }
 
-      const errorClass =
-        Config.mode === "zen" ? "" : input !== word ? "error" : "";
+      const isIncorrectWord = input !== word;
+      const isLastWord = i === inputHistoryLength - 1;
+      const isTimedTest =
+        Config.mode === "time" ||
+        (Config.mode === "custom" && CustomText.getLimitMode() === "time") ||
+        (Config.mode === "custom" && CustomText.getLimitValue() === 0);
+      const isPartiallyCorrect = word.substring(0, input.length) === input;
+
+      const shouldShowError =
+        Config.mode !== "zen" &&
+        !(isLastWord && isTimedTest && isPartiallyCorrect);
+
+      const errorClass = isIncorrectWord && shouldShowError ? "error" : "";
 
       if (corrected !== undefined && corrected !== "") {
         const correctedChar = !containsKorean