feat: Add guest mode authentication and fix dashboard telemetry display

[gagan-devv]

🎯 Overview

This PR introduces guest mode functionality for anonymous users and fixes critical dashboard telemetry issues. Users can now try predictions without registration, and the dashboard correctly displays real-time sensor data.

✨ Features

Guest Mode Authentication

• 🎭 Anonymous access with 30-minute JWT tokens
• 🔓 Guest-specific prediction endpoints (no registration required)
• 🚫 Middleware protection for user-only routes
• 📱 Seamless guest UI flow in mobile app

Dashboard Telemetry Fix

• 📊 Real-time sensor data now displays correctly
• 🔄 Fixed API response field name normalization (n/p/k → N/P/K)
• 🐛 Resolved "Choose from History" button not showing results
• ✅ Fixed zero value rendering in StatCard components

🔧 Technical Changes

Backend (Go)

• Added /api/v1/auth/guest endpoint for guest token generation
• Created RequireUser() middleware to block guest access to protected routes
• Implemented guest prediction endpoints: /api/v1/guest/predict/{crop,fertilizer,suitability}
• Fixed ONNX inference to handle int64 output tensors
• Updated fertilizer model labels to match actual outputs

Mobile App (React Native)

• Implemented guest authentication flow with isGuest flag in authStore
• Added guest API methods (guestPredictCrop, guestPredictFertilizer, etc.)
• Fixed dashboard to normalize nested API response structure
• Enhanced console logging for debugging sensor data flow
• Added guest badge indicator and restricted navigation
• Fixed StatCard value rendering for zero/null values

ML Models

• Re-exported ONNX models with int64 outputs (ArgMax + Identity nodes)
• Crop model: 23 classes with correct tensor names
• Fertilizer model: 7 classes with updated labels
• Added validation and conversion scripts

🐛 Bug Fixes

• Fixed dashboard telemetry showing -- instead of actual sensor values
• Fixed "Choose from History" button not displaying prediction results
• Fixed "Predict Again" button to properly clear results and reset state
• Resolved race condition in guest login flow
• Fixed nested API response handling from backend

📚 Documentation

• Updated README.md with new architecture and v2.0 features
• Documented guest mode functionality and API endpoints
• Added comprehensive API endpoint documentation
• Updated tech stack and project structure

🧪 Testing

• ✅ All mobile tests pass
• ✅ Backend endpoints tested and verified
• ✅ Guest mode fully functional end-to-end
• ✅ Dashboard telemetry displays real sensor data

📸 Screenshots

Before

• Dashboard showing -- for all telemetry values
• No guest mode option

After

• Dashboard displaying real sensor data (Temperature: 28.1°C, Humidity: 19%, etc.)
• Guest mode accessible from landing page
• Predictions work without registration

🔄 Migration Notes

No breaking changes. Existing users are unaffected. Guest tokens are separate from user tokens.

📝 Checklist

• Code follows project style guidelines
• Tests pass successfully
• Documentation updated
• No breaking changes
• Commit messages follow conventional commits
• Branch is up to date with base branch

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Files Changed: 28 files (+2511, -623)
Commit: 6c76926