Add local-device setup documentation and configuration

Author: david0154

QUICK_SETUP_LOCAL.md

@@ -0,0 +1,116 @@
+# ⚡ DAVID AI - 5 Minute Local Setup
+
+## 🎯 What You Get
+
+✅ **Google Login** (No backend needed)  
+✅ **Local Chat Storage** (120-day auto-cleanup)  
+✅ **AI Models** (Auto-download from Hugging Face)  
+✅ **Device Only** (Zero cloud sync)  
+✅ **Open Source** (No backend code needed)  
+
+---
+
+## 🚀 Setup Steps
+
+### Step 1: Get Google Client ID (3 min)
+```
+1. Go to https://firebase.google.com/console
+2. Create new project "DAVID-AI"
+3. Add Android app
+4. Get Web Client ID from Settings
+```
+
+### Step 2: Update Code (1 min)
+```kotlin
+// File: GoogleAuthManager.kt (Line 22)
+.requestIdToken("YOUR_WEB_CLIENT_ID") // ← Paste here
+```
+
+### Step 3: Build & Run (1 min)
+```bash
+./gradlew installDebug
+```
+
+### Step 4: First Launch (auto)
+- App downloads models
+- Google Sign-In works
+- Chat stored locally
+- **Done!**
+
+---
+
+## 📊 Storage Breakdown
+
+```
+Chat History:  ~1-10 MB (auto-deletes after 120 days)
+Models:        ~1.5-3 GB (based on device RAM)
+App Size:      ~50 MB
+
+Total: 1.5-3.5 GB
+```
+
+---
+
+## 🔧 What Changed from Backend Version
+
+| Feature | Backend | Local |
+|---------|---------|-------|
+| Storage | Cloud | Device |
+| Chat | Cloud DB | SQLite |
+| Models | Server | Hugging Face |
+| Auth | Custom | Google |
+| Sync | API | None |
+| Cost | $$/month | $0 |
+| Privacy | Server | All Local |
+
+---
+
+## ✨ Core Files
+
+✅ `auth/GoogleAuthManager.kt` - Google login  
+✅ `storage/ChatHistoryManager.kt` - Local chat storage  
+✅ `models/ModelManager.kt` - Model management  
+✅ `config/ModelConfig.kt` - Model URLs  
+
+---
+
+## 🎓 Usage Examples
+
+### Save Chat
+```kotlin
+chatHistoryManager.saveChatMessage(
+    userId = "user123",
+    userMessage = "Hello",
+    assistantResponse = "Hi!"
+)
+```
+
+### Get History
+```kotlin
+val history = chatHistoryManager.getRecentHistory(userId)
+```
+
+### Download Models
+```kotlin
+val models = modelManager.getRecommendedModels()
+modelManager.downloadModel(model) { progress ->
+    println("$progress%")
+}
+```
+
+---
+
+## ✅ Checklist
+
+- [ ] Firebase project created
+- [ ] Web Client ID obtained
+- [ ] Code updated with ID
+- [ ] Build successful
+- [ ] APK installs
+- [ ] Google login works
+- [ ] Models download
+- [ ] Chat saves locally
+
+---
+
+**Zero Backend. 100% Local. Fully Private.**