fix: 修复Agent Loop工具调用重复问题，移除web_fetch截断

- 新增工具调用缓存机制，避免重复调用相同工具+参数
- 新增同轮内重复检测和跨轮次重复检测，连续两轮相同调用自动终止循环
- TOOLS_USAGE_GUIDE 新增第8条严禁重复调用规则
- web_fetch 默认不截断(max_chars=0)，返回完整内容
- 移除 tool-registry.ts executeTool 中重复的 logToolStart 调用

src/main/tool-handlers.ts

@@ -433,9 +433,9 @@ export async function handleWebFetch(params: { url: string; max_chars?: number;
       return { success: false, error: '仅支持 http/https 协议' };
     }
 
-    const maxChars = params.max_chars || 10000;
+    const maxChars = params.max_chars || 0; // 0 = 不截断，返回全部内容
 
-    sendLog('info', `🌐 web_fetch`, `${url} (${maxChars} chars)`);
+    sendLog('info', `🌐 web_fetch`, `${url} (${maxChars > 0 ? maxChars + ' chars' : '完整内容'})`);
     const resp = await fetch(url, {
       headers: { 'User-Agent': 'MetonaOllama/1.0' },
       signal: AbortSignal.timeout(15000)
@@ -466,7 +466,7 @@ export async function handleWebFetch(params: { url: string; max_chars?: number;
         .trim();
     }
 
-    const truncated = text.length > maxChars;
+    const truncated = maxChars > 0 && text.length > maxChars;
     if (truncated) text = text.slice(0, maxChars);
 
     sendLog('success', `🌐 web_fetch 完成`, `${resp.status} | ${text.length} chars${truncated ? ' (已截断)' : ''}`);