feat(tui): wire live gRPC data into watch dashboard
- Add data_fetcher.rs: StateUpdate enum, DataFetcher with 7 background
stream/poller tasks (training metrics, system status, account state,
executions, portfolio summary, download status, risk metrics)
- Wire event_loop.rs: FoxhuntClient connect, DataFetcher start,
mpsc channel drain each tick, apply_update() for all 11 variants
- Add connection status indicator to status bar (LIVE/CONNECTING/OFFLINE)
- Replace mock data defaults with empty vecs/zeros in state.rs
- Add ConnectionStatus enum (Connecting/Connected/Reconnecting/Error)
- Exponential backoff (1s → 30s) on stream errors with auto-reconnect
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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