feat(desktop): add Training page with 5 tabs (ADR-057)
Implements the Training & Models page with tabbed navigation:
- Datasets tab: Download/import datasets, preview samples
- Models tab: Browse architectures, manage checkpoints, export ONNX
- Training tab: Configure training, GPU detection, live progress
- RuVector tab: Module config (MinCut, Attention, Temporal, Solver)
- Metrics tab: Loss curves, evaluation metrics, per-joint accuracy
Features:
- GPU detection status display (CUDA/Metal)
- Live training progress with Tauri events
- RuVector module enable/disable and parameter tuning
- Training presets (Low Latency, High Accuracy, Balanced)
- Export metrics to CSV/JSON/TensorBoard
- Mock data for demonstration when backend not implemented
Ref: ADR-057
Co-Authored-By: claude-flow <ruv@ruv.net>
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