add paper trading: mark a setup as taken, track open P&L, sell

New paper_trades table (migration 007) + service/router. "Mark as taken" on each
setup card (shares prefilled from position sizing, entry from current price, both
editable) records a simulated trade. Overview gains an Open Trades table that
marks each position to the latest close — P&L in $, %, and R-multiples — with a
total unrealized P&L footer and a Sell button to close at the current price.
Closed trades are retained for future realized-P&L reporting.

Deploy: alembic upgrade (new paper_trades table).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/schemas/paper_trade.py

@@ -0,0 +1,35 @@
+"""Schemas for paper trades."""
+
+from __future__ import annotations
+
+from datetime import datetime
+
+from pydantic import BaseModel, Field
+
+
+class PaperTradeCreate(BaseModel):
+    symbol: str = Field(..., min_length=1, max_length=10)
+    direction: str = Field(..., pattern=r"^(long|short)$")
+    entry_price: float = Field(..., gt=0)
+    shares: float = Field(..., gt=0)
+    stop_loss: float = Field(..., gt=0)
+    target: float = Field(..., gt=0)
+
+
+class PaperTradeClose(BaseModel):
+    close_price: float | None = Field(default=None, gt=0)
+
+
+class PaperTradeResponse(BaseModel):
+    id: int
+    symbol: str
+    direction: str
+    entry_price: float
+    shares: float
+    stop_loss: float
+    target: float
+    status: str
+    opened_at: datetime
+    close_price: float | None = None
+    closed_at: datetime | None = None
+    current_price: float | None = None