add position-size calculator to the recommendation panel

Risk-based sizing on each setup card: shares = floor((account × risk%) /
|entry − stop|), with position value and dollars-at-risk. Account size and
per-trade risk % are editable inline and persisted in localStorage. Flags when
a position would exceed the account (needs margin). Frontend-only.

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

frontend/src/hooks/useRiskSettings.ts

@@ -0,0 +1,37 @@
+import { useCallback, useEffect, useState } from 'react';
+
+export interface RiskSettings {
+  accountSize: number;
+  riskPct: number;
+}
+
+const STORAGE_KEY = 'risk-settings';
+const DEFAULTS: RiskSettings = { accountSize: 10000, riskPct: 1 };
+
+/** Account size + per-trade risk %, persisted in localStorage (per browser). */
+export function useRiskSettings() {
+  const [settings, setSettings] = useState<RiskSettings>(() => {
+    try {
+      const raw = localStorage.getItem(STORAGE_KEY);
+      if (raw) return { ...DEFAULTS, ...JSON.parse(raw) };
+    } catch {
+      /* ignore malformed storage */
+    }
+    return DEFAULTS;
+  });
+
+  useEffect(() => {
+    try {
+      localStorage.setItem(STORAGE_KEY, JSON.stringify(settings));
+    } catch {
+      /* ignore quota/availability errors */
+    }
+  }, [settings]);
+
+  const update = useCallback(
+    (patch: Partial<RiskSettings>) => setSettings((s) => ({ ...s, ...patch })),
+    [],
+  );
+
+  return { settings, update };
+}