Add Procrastinate sample app

[StephaneDelcroix]

Summary

This PR adds Procrastinate, a fun anti-productivity app that demonstrates several advanced .NET MAUI features including MEAI (Microsoft.Extensions.AI) integration.

MEAI Features Demonstrated

• IChatClient — On-device AI via AppleIntelligenceChatClient (iOS/macOS)
• IChatClient — Cloud AI via OpenAI-compatible adapter (Groq/Llama)
• IEmbeddingGenerator — NLEmbeddingGenerator for quality scoring of generated excuses
• Multi-Agent Pipeline — 3-agent chain (Researcher→Writer→Editor) with reasoning panel
• BYOM (Bring Your Own Model) — Any OpenAI-compatible endpoint (Ollama, LM Studio, etc.)
• Embedded ONNX Model — In-process OnnxRuntimeGenAI with HuggingFace model download
• Hybrid AI Switching — Settings UI to switch between local/cloud/pipeline/custom/embedded modes

Other Features Demonstrated

• Shell Navigation — Tab-based navigation with 5 main pages
• Localization — Full translation in 7 languages (English, French, Spanish, Portuguese, Dutch, Czech, Ukrainian)
• Custom Theming — Nord color palette with dark/light theme support
• Mini-Games — 9 games including TicTacToe with AI opponent (via IChatClient)
• XAML Source Generator — Uses MauiXamlInflator=SourceGen
• Plugin.Maui.Audio — Sound effects for Simon Says game
• SecureStorage — API keys stored securely (Keychain/EncryptedSharedPrefs)

Hackday Challenge Levels Covered

• 🟢 Basic: Local AI via AppleIntelligenceChatClient + cloud AI via Groq
• 🟡 Advanced: Hybrid model switching, NLEmbedding quality scoring, BYOM endpoints
• 🟠 Agent Framework: 3-agent pipeline with reasoning display
• 🔴 Freestyle: Embedded ONNX model (Phi-3 Mini) running entirely on-device

Original Repository

https://github.com/StephaneDelcroix/procrastinate

Testing

# iOS (requires .NET 10 SDK + dotnet10 nightly feed)
dotnet build -f net10.0-ios

# Android
dotnet build -f net10.0-android

# macOS
dotnet build -f net10.0-maccatalyst

[StephaneDelcroix]

🔄 Updated: Full MEAI Migration + Advanced AI Features

This PR has been updated with a complete migration from the custom FMWrapper native bridge to Microsoft.Extensions.AI (MEAI). Changes include:

Core Migration

• Replaced ~200 lines of P/Invoke/Swift bridge code with IChatClient abstraction
• On-device: AppleIntelligenceChatClient from Microsoft.Maui.Essentials.AI
• Cloud: OpenAI.OpenAIClient.AsIChatClient() targeting Groq (OpenAI-compatible)
• Registered via DI in MauiProgram.cs

Advanced Features

• NLEmbedding Quality Scoring — IEmbeddingGenerator cosine similarity against golden excuses, with retry on low quality
• BYOM — Custom endpoint support for Ollama, LM Studio, vLLM, etc.
• 3-Agent Pipeline — Researcher→Writer→Editor chain with collapsible reasoning panel showing each agent's output
• Embedded ONNX — OnnxRuntimeGenAI for in-process Phi-3 Mini (download from HuggingFace)

Code Quality (from multi-model code review)

• Thread-safe ONNX client singleton with lock + active inference counter
• API keys migrated to SecureStorage (Keychain/EncryptedSharedPrefs)
• Cached golden embeddings, epsilon-guarded cosine similarity
• UI callback cleanup in OnDisappearing to prevent page leaks
• Atomic downloads with .tmp rename, concurrency guard via SemaphoreSlim
• Friendly error messages instead of raw exception text