engine: a Hanja word shows once, as every other candidate does

hanjaquery was the only query that assigned dictprefix's output straight
into im.kouho; emojiquery, dictqjp and katakouho all go through
addkouho, which is the only place a duplicate is dropped.  Two readings
under one prefix can carry the same word, and 198 of the 61,479 one- and
two-syllable prefixes in hanja.dict do: 게 listed 偈句 at rows 8 and 9,
개근 listed 皆勤狀 twice in five.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/engine_test.c

@@ -2072,6 +2072,8 @@ engine_hanja_word_prefix(struct ct *t)
 	Str com;
 
 	hanjabegin(&f, LangKO);
+	/* Two readings under one prefix may share a word; it shows once. */
+	setdict(f.dictlang->dict, "민민", "民");
 	sclear(&com);
 	if(!CT_CHECK(t, keystroke('h', Mctrl, &com)) ||
 	   !typekeys(t, "als", &com))