Fix incorrect pinyin highlight for polyphonic characters (e.g. 核查 with hecha/heia)

[Copilot]

Searching for 核查 using full pinyin (hecha) or XiaoHe double pinyin (heia) produced no highlights because the ToolGood library's GetPinyinList() applies context-sensitive disambiguation across the whole input string — incorrectly returning "Zha" for 查 in "核查" instead of "Cha". This caused the translated form to be "He Zha" / "he va" (XiaoHe), which doesn't match the user's query.

Changes

• PinyinAlphabet.cs — BuildCacheFromContent: Replace bulk WordsHelper.GetPinyinList(content) with per-character WordsHelper.GetAllPinyin(c, false)[0], which returns pronunciations sorted by frequency and avoids erroneous cross-character disambiguation.

// Before — wrong: GetPinyinList("核查") → ["He", "Zha"]
var resultList = WordsHelper.GetPinyinList(content);
var translated = _settings.UseDoublePinyin ? ToDoublePinyin(resultList[i]) : resultList[i];

// After — correct: GetAllPinyin('查') → ["Cha", "Zha"] → uses "Cha"
var allPinyins = WordsHelper.GetAllPinyin(content[i], false);
var pinyin = allPinyins.Count > 0 ? allPinyins[0] : WordsHelper.GetPinyinList(content[i].ToString(), false)[0];
var translated = _settings.UseDoublePinyin ? ToDoublePinyin(pinyin) : pinyin;

With the fix, 核查 translates to "He Cha" (full pinyin) / "he ia" (XiaoHe), correctly matching and highlighting both characters.

• Fixes BUG: Incorrect highlight when using pinyin in some cases #4455

[Jack251970]

I think we can continue this work in #4544 instead of this new PR.