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/hooks/usePaperTrades.ts

@@ -0,0 +1,38 @@
+import { useMutation, useQuery, useQueryClient } from '@tanstack/react-query';
+import * as api from '../api/paperTrades';
+import { useToast } from '../components/ui/Toast';
+
+export function usePaperTrades(status?: 'open' | 'closed') {
+  return useQuery({
+    queryKey: ['paper-trades', status ?? 'all'],
+    queryFn: () => api.listPaperTrades(status),
+    refetchInterval: 60_000,
+  });
+}
+
+export function useCreatePaperTrade() {
+  const qc = useQueryClient();
+  const { addToast } = useToast();
+  return useMutation({
+    mutationFn: (body: api.CreatePaperTradeBody) => api.createPaperTrade(body),
+    onSuccess: (t) => {
+      qc.invalidateQueries({ queryKey: ['paper-trades'] });
+      addToast('success', `Taken: ${t.shares} ${t.symbol} ${t.direction.toUpperCase()} @ ${t.entry_price}`);
+    },
+    onError: (e: Error) => addToast('error', e.message || 'Failed to take trade'),
+  });
+}
+
+export function useClosePaperTrade() {
+  const qc = useQueryClient();
+  const { addToast } = useToast();
+  return useMutation({
+    mutationFn: ({ id, closePrice }: { id: number; closePrice?: number }) =>
+      api.closePaperTrade(id, closePrice),
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: ['paper-trades'] });
+      addToast('success', 'Trade closed.');
+    },
+    onError: (e: Error) => addToast('error', e.message || 'Failed to close trade'),
+  });
+}