feat: implement WebSocket trade stream handler with reconnection

- Add TradeEvent dataclass for trade data from WebSocket feed
- Implement TradeStreamHandler with async WebSocket streaming
- Add automatic reconnection with exponential backoff (1s-30s)
- Support event/market filtering for targeted subscriptions
- Include connection state management and statistics tracking
- Add websockets>=12.0 dependency

Acceptance Criteria:
- [x] TradeStreamHandler class using websockets library
- [x] Connects to Polymarket WSS endpoint
- [x] Subscribes to market trade channel on connection
- [x] Parses trade messages into TradeEvent dataclass
- [x] Implements heartbeat/ping-pong for connection health
- [x] Auto-reconnects on disconnect with exponential backoff
- [x] Emits events via callback pattern
- [x] Logs connection state changes

Closes #3

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/polymarket_insider_tracker/ingestor/models.py

@@ -1,9 +1,9 @@
 """Data models for the ingestor module."""
 
 from dataclasses import dataclass, field
-from datetime import datetime
+from datetime import datetime, timezone
 from decimal import Decimal
-from typing import Any
+from typing import Any, Literal
 
 
 @dataclass(frozen=True)
@@ -138,3 +138,91 @@ class Orderbook:
         if self.best_bid is not None and self.best_ask is not None:
             return (self.best_bid + self.best_ask) / 2
         return None
+
+
+@dataclass(frozen=True)
+class TradeEvent:
+    """Represents a trade event from the Polymarket WebSocket feed.
+
+    This captures all the information about a single trade execution,
+    including the market, wallet, trade details, and metadata.
+    """
+
+    # Core trade identifiers
+    market_id: str  # conditionId - the market/CTF condition ID
+    trade_id: str  # transactionHash - unique trade identifier
+    wallet_address: str  # proxyWallet - trader's wallet address
+
+    # Trade details
+    side: Literal["BUY", "SELL"]
+    outcome: str  # Human-readable outcome (e.g., "Yes", "No")
+    outcome_index: int  # Index of the outcome (0 or 1)
+    price: Decimal
+    size: Decimal  # Number of shares traded
+    timestamp: datetime
+
+    # Asset information
+    asset_id: str  # ERC1155 token ID
+
+    # Market metadata
+    market_slug: str = ""
+    event_slug: str = ""
+    event_title: str = ""
+
+    # Trader metadata (optional - may not be available for all trades)
+    trader_name: str = ""
+    trader_pseudonym: str = ""
+
+    @classmethod
+    def from_websocket_message(cls, data: dict[str, Any]) -> "TradeEvent":
+        """Create a TradeEvent from a WebSocket activity/trade message.
+
+        Args:
+            data: The payload from a WebSocket trade message.
+
+        Returns:
+            TradeEvent instance.
+        """
+        # Parse timestamp - it's a Unix timestamp in seconds
+        raw_timestamp = data.get("timestamp", 0)
+        if isinstance(raw_timestamp, int):
+            timestamp = datetime.fromtimestamp(raw_timestamp, tz=timezone.utc)
+        else:
+            timestamp = datetime.now(timezone.utc)
+
+        # Parse side - normalize to uppercase
+        side_raw = str(data.get("side", "BUY")).upper()
+        side: Literal["BUY", "SELL"] = "BUY" if side_raw == "BUY" else "SELL"
+
+        return cls(
+            market_id=str(data.get("conditionId", "")),
+            trade_id=str(data.get("transactionHash", "")),
+            wallet_address=str(data.get("proxyWallet", "")),
+            side=side,
+            outcome=str(data.get("outcome", "")),
+            outcome_index=int(data.get("outcomeIndex", 0)),
+            price=Decimal(str(data.get("price", 0))),
+            size=Decimal(str(data.get("size", 0))),
+            timestamp=timestamp,
+            asset_id=str(data.get("asset", "")),
+            market_slug=str(data.get("slug", "")),
+            event_slug=str(data.get("eventSlug", "")),
+            event_title=str(data.get("title", "")),
+            trader_name=str(data.get("name", "")),
+            trader_pseudonym=str(data.get("pseudonym", "")),
+        )
+
+    @property
+    def is_buy(self) -> bool:
+        """Return True if this is a buy trade."""
+        return self.side == "BUY"
+
+    @property
+    def is_sell(self) -> bool:
+        """Return True if this is a sell trade."""
+        return self.side == "SELL"
+
+    @property
+    def notional_value(self) -> Decimal:
+        """Return the notional value of the trade (price * size)."""
+        return self.price * self.size