fix(web): 聊天列表恢复项目符号，收紧定义列表，压思考条间距（BUG-962/963/964）

frontend/src/lib/chat-definition-lists.ts

@@ -1,17 +1,26 @@
 const FENCE = /(```[\s\S]*?```)/;
 const DEFINITION_LINE = /^(.{2,80}?)[：:](.+)$/u;
+const SENTENCE_END = /[。！？；!?;]/u;
+const BODY_MAX_CHARS = 40;
 
 function isSkippableLine(line: string): boolean {
   return /^(#{1,6}\s|>\s|[-*+]\s|\d+[.)]\s|\|)/.test(line) || line.startsWith("```");
 }
 
+function isSingleSentence(text: string): boolean {
+  return !SENTENCE_END.test(text.replace(/[。！？；!?;]$/u, ""));
+}
+
 function isDefinitionLine(block: string): boolean {
   const trimmed = block.trim();
   if (!trimmed || trimmed.includes("\n") || isSkippableLine(trimmed)) return false;
   const match = DEFINITION_LINE.exec(trimmed);
   if (!match) return false;
+  const term = match[1]?.trim() ?? "";
   const body = match[2]?.trim() ?? "";
-  return body.length >= 4;
+  if (body.length < 4 || body.length > BODY_MAX_CHARS) return false;
+  if (SENTENCE_END.test(term)) return false;
+  return isSingleSentence(body);
 }
 
 function toListItem(block: string): string {