Add Voxtral Realtime Windows WPF application

[seyeong-han]

Summary

Adds a Windows WPF (.NET 8) desktop application for Voxtral Realtime — a real-time speech-to-text transcription tool powered by ExecuTorch. This is the Windows counterpart to the existing macOS SwiftUI application.

Key Features

• Real-time transcription — Live speech-to-text using the Voxtral model running locally via ExecuTorch
• Dictation mode — Speak and auto-paste transcribed text into any target application via clipboard
• Silence detection — Peak-based audio level monitoring with configurable silence threshold and timeout for auto-stop
• Text processing pipeline — Post-processing with configurable text replacements and snippet expansion
• Session history — Persistent transcript storage with search and browsing
• Global hotkey — System-wide keyboard shortcut to start/stop transcription
• MVVM architecture — Clean separation using CommunityToolkit.Mvvm with ObservableObject view models

Architecture

VoxtralRealtime/
├── Models/           # Data models (Session, Snippet, ReplacementEntry, Enums)
├── Converters/       # WPF value converters
├── Services/         # Core services
│   ├── RunnerBridge.cs         # ExecuTorch model bridge
│   ├── AudioCaptureService.cs  # NAudio-based mic capture
│   ├── ClipboardPasteService.cs # Win32 clipboard + paste
│   ├── GlobalHotkeyService.cs  # System-wide hotkey registration
│   ├── TextPipeline.cs         # Post-processing pipeline
│   ├── PersistenceService.cs   # JSON file storage
│   └── AppLogger.cs            # File-based logging
├── ViewModels/       # MVVM view models
│   ├── TranscriptStoreViewModel.cs  # Central state management
│   ├── DictationViewModel.cs        # Dictation flow + silence monitor
│   ├── SettingsViewModel.cs         # App configuration
│   ├── ReplacementStoreViewModel.cs # Text replacements
│   └── SnippetStoreViewModel.cs     # Text snippets
├── Views/            # WPF XAML views
│   ├── MainWindow              # Shell with sidebar + detail layout
│   ├── WelcomeView             # Home/landing page
│   ├── TranscriptView          # Live transcript display
│   ├── SidebarView             # Navigation sidebar
│   ├── RecordingControlsBar    # Toolbar (transcribe/pause/done)
│   ├── DictationWindow         # Floating dictation overlay
│   ├── AudioLevelControl       # Real-time audio level meter
│   ├── SettingsView            # Configuration UI
│   └── *ManagementViews        # Replacement & snippet editors
└── Resources/        # Styles and assets

Also Included

• .gitignore updated with .NET/C# build artifact rules (bin/, obj/, publish/, etc.)
• build.bat for release builds
• upload_models.py helper for model distribution
• README.md with setup and build instructions

Test Plan

• Built and tested manually on Windows 10/11 with .NET 8
• Verified real-time transcription, dictation auto-paste, silence detection, and session persistence

[mergennachin]

@claude Review this PR