docs: Add Windows quick start guide

WINDOWS_QUICK_START.md

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+# 🚀 Windows Quick Start Guide
+
+**Get SecondVoice running on Windows in 5 steps!**
+
+---
+
+## ⚡ Prerequisites (5-10 minutes)
+
+### 1. Install Visual Studio 2022 Community (Free)
+👉 https://visualstudio.microsoft.com/downloads/
+
+During installation, select:
+- ✅ **Desktop development with C++**
+
+### 2. Install vcpkg
+Open **PowerShell as Administrator**:
+```powershell
+cd C:\
+git clone https://github.com/microsoft/vcpkg.git
+cd vcpkg
+.\bootstrap-vcpkg.bat
+setx VCPKG_ROOT "C:\vcpkg"
+```
+
+**⚠️ Important**: Close and reopen PowerShell after setting `VCPKG_ROOT`
+
+---
+
+## 🔧 Build SecondVoice (1-2 minutes)
+
+### 1. Clone the project
+```powershell
+cd "E:\Users\Alexis Trouvé\Documents\Projets"
+git clone <repository-url> secondvoice
+cd secondvoice
+```
+
+### 2. Create your API keys file
+```powershell
+copy .env.example .env
+notepad .env
+```
+
+Add your keys:
+```
+OPENAI_API_KEY=sk-...
+ANTHROPIC_API_KEY=sk-ant-...
+```
+
+### 3. Build!
+```powershell
+build.bat --release
+```
+
+**First build takes 5-10 minutes** (downloads dependencies).
+
+---
+
+## ▶️ Run SecondVoice
+
+```powershell
+cd build\windows-release\Release
+SecondVoice.exe
+```
+
+**That's it!** 🎉
+
+---
+
+## 🎯 What to Expect
+
+1. **ImGui window opens** with "SecondVoice - Live Translation"
+2. **Recording starts** automatically
+3. **Speak Chinese** into your microphone
+4. **Transcription appears** in blue (中文)
+5. **Translation appears** in green (FR)
+6. **Click "STOP RECORDING"** when done
+7. **Audio saved** to `recordings/` folder
+
+---
+
+## ⚙️ Quick Configuration
+
+Edit `config.json` to customize:
+
+```json
+{
+  "audio": {
+    "chunk_duration_seconds": 10  // Lower = faster updates (5-30s)
+  },
+  "whisper": {
+    "model": "gpt-4o-mini-transcribe",  // Or "gpt-4o-transcribe" for best quality
+    "prompt": "Add your context here (names, topics, etc.)"
+  }
+}
+```
+
+---
+
+## 🐛 Troubleshooting
+
+### "VCPKG_ROOT not set"
+```powershell
+setx VCPKG_ROOT "C:\vcpkg"
+# Restart PowerShell
+```
+
+### "cl.exe not found"
+Open **Visual Studio Developer Command Prompt** instead of regular PowerShell.
+
+### "No audio device found"
+1. Check microphone is connected
+2. Go to **Settings → Sound → Input**
+3. Test your microphone
+
+### Build fails with dependency errors
+```powershell
+build.bat --clean --release
+```
+
+---
+
+## 📊 Costs
+
+- **Whisper API**: $0.006/minute (~$0.36/hour)
+- **Claude API**: ~$0.04/hour
+- **Total**: **~$0.40/hour** of recording
+
+Very affordable for the value! 💰
+
+---
+
+## 📚 Need More Help?
+
+- **Full Windows guide**: `docs/build_windows.md`
+- **General docs**: `docs/next_steps.md`
+- **Whisper upgrade**: `docs/whisper_upgrade.md`
+
+---
+
+## 🎉 You're Ready!
+
+Test it with:
+1. **Sample Chinese audio** (YouTube, recordings)
+2. **Real conversation** with Chinese speakers
+3. **Important meeting** where you need translation
+
+Good luck with your first meeting! 🚀
+
+---
+
+*Quick start version - Last updated: 20 novembre 2025*