fix: add error handling for API failures with graceful error messages

[D2758695161]

Fix: Add error handling for API failures

Problem

Issue #5 reported that https://api.vvhan.com/api is inaccessible, causing all MCP tools to crash with unhandled errors when the external API is down.

Solution

1. src/utils/fetch.ts - Added try-catch error handling with timeout support (fetchWithTimeout helper with 10s timeout) to all API functions. When the API fails, returns a graceful error response instead of throwing.

2. All tool files (weiboHotspots.ts, internetHotspotsAggregator.ts, todayHeadlinesHotspots.ts, paperNewsHotspots.ts, horoscope.ts, dailyEnglishSentence.ts) - Updated to check for success: false and empty data arrays, returning user-friendly Chinese error messages like:

   • "获取微博热搜失败: [error details]"
   • "无法获取微博热搜数据，请稍后重试或检查网络连接"

Benefits

• MCP server no longer crashes when external API is unreachable
• Users get clear error messages instead of silent failures
• Timeout protection (10s) prevents hanging requests

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