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>

frontend/src/api/paperTrades.ts

@@ -0,0 +1,29 @@
+import apiClient from './client';
+import type { PaperTrade } from '../lib/types';
+
+export function listPaperTrades(status?: 'open' | 'closed') {
+  return apiClient
+    .get<PaperTrade[]>('paper-trades', { params: status ? { status } : {} })
+    .then((r) => r.data);
+}
+
+export interface CreatePaperTradeBody {
+  symbol: string;
+  direction: 'long' | 'short';
+  entry_price: number;
+  shares: number;
+  stop_loss: number;
+  target: number;
+}
+
+export function createPaperTrade(body: CreatePaperTradeBody) {
+  return apiClient.post<PaperTrade>('paper-trades', body).then((r) => r.data);
+}
+
+export function closePaperTrade(id: number, closePrice?: number) {
+  return apiClient
+    .post<{ id: number; status: string }>(`paper-trades/${id}/close`, {
+      close_price: closePrice ?? null,
+    })
+    .then((r) => r.data);
+}