feat: market-data-service for SenpAI trading agent

New service: real-time market data collection with unified event model.

Architecture:
- Domain events: TradeEvent, QuoteEvent, BookL2Event, HeartbeatEvent
- Provider interface: MarketDataProvider ABC with connect/subscribe/stream/close
- Async EventBus with fan-out to multiple consumers

Providers:
- BinanceProvider: public WebSocket (trades + bookTicker), no API key needed,
  auto-reconnect with exponential backoff, heartbeat timeout detection
- AlpacaProvider: IEX real-time data + paper trading auth,
  dry-run mode when no keys configured (heartbeats only)

Consumers:
- StorageConsumer: SQLite (via SQLAlchemy async) + JSONL append-only log
- MetricsConsumer: Prometheus counters, latency histograms, events/sec gauge
- PrintConsumer: sampled structured logging (1/100 events)

CLI: python -m app run --provider binance --symbols BTCUSDT,ETHUSDT
HTTP: /health, /metrics (Prometheus), /latest?symbol=XXX

Tests: 19/19 passed (Binance parse, Alpaca parse, bus smoke tests)

Config: pydantic-settings + .env, all secrets via environment variables.
Co-authored-by: Cursor <cursoragent@cursor.com>

services/market-data-service/app/providers/__init__.py

@@ -0,0 +1,57 @@
+"""
+Market data provider interface and registry.
+
+To add a new provider:
+1. Create providers/your_provider.py
+2. Subclass MarketDataProvider
+3. Register in PROVIDER_REGISTRY below
+"""
+from __future__ import annotations
+
+from abc import ABC, abstractmethod
+from typing import AsyncIterator
+
+from app.domain.events import Event
+
+
+class MarketDataProvider(ABC):
+    """
+    Base class for all market-data feed adapters.
+
+    Lifecycle:  connect() → subscribe() → stream() → close()
+    """
+
+    name: str = "unknown"
+
+    @abstractmethod
+    async def connect(self) -> None:
+        """Establish connection to the data source."""
+
+    @abstractmethod
+    async def subscribe(self, symbols: list[str]) -> None:
+        """Subscribe to symbols. May be called after reconnect."""
+
+    @abstractmethod
+    async def stream(self) -> AsyncIterator[Event]:
+        """Yield normalized domain events. Must handle reconnect internally."""
+        yield  # type: ignore
+
+    @abstractmethod
+    async def close(self) -> None:
+        """Graceful shutdown."""
+
+
+def get_provider(name: str) -> MarketDataProvider:
+    """Factory: instantiate provider by name."""
+    from app.providers.binance import BinanceProvider
+    from app.providers.alpaca import AlpacaProvider
+
+    registry: dict[str, type[MarketDataProvider]] = {
+        "binance": BinanceProvider,
+        "alpaca": AlpacaProvider,
+    }
+    cls = registry.get(name.lower())
+    if cls is None:
+        available = ", ".join(registry.keys())
+        raise ValueError(f"Unknown provider '{name}'. Available: {available}")
+    return cls()