feat: add vision, TTS, and browser tools (17 tools total)
- VisionTool: image analysis via Z.AI GLM-4V multimodal API
- TTSTool: text-to-speech via node-edge-tts (free, auto-sends audio to chat)
- BrowserTool: web page content extraction via cheerio (strips HTML, extracts text)
- All 3 wired into tools/index.js + bot tool definitions + handlers
- TTS handler auto-sends generated audio as voice message to chat
