Add shadcn/ui design system, theme, and base components

Install shadcn/ui with base-nova style, tailwind-merge, tw-animate-css,
and font packages. Add oklch-based light/dark theme in index.css and
17 base UI components (button, card, dialog, table, tabs, etc.) plus
shared lib utilities (format, colors, cn) and useSettings hook.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/hooks/useSettings.ts

@@ -0,0 +1,55 @@
+import { useEffect, useState, useCallback } from 'react';
+import {
+  getSettings,
+  updateSettings,
+  type UserSettingsData,
+  type SectionSettings,
+} from '../api';
+
+const DEFAULT_SETTINGS: UserSettingsData = {
+  dashboard: {
+    sections: {
+      crc_accounts: { label: 'CRC Accounts', color: 'primary', cardColor: 'primary', visible: true, order: 0, expanded: false },
+      usd_accounts: { label: 'USD Accounts', color: 'chart-1', cardColor: 'chart-1', visible: true, order: 1, expanded: false },
+      pension: { label: 'Pension', color: 'chart-2', cardColor: 'chart-2', visible: true, order: 2, expanded: false },
+      savings: { label: 'Savings', color: 'chart-3', cardColor: 'chart-3', visible: true, order: 3, expanded: false },
+      liabilities: { label: 'Liabilities', color: 'destructive', cardColor: 'destructive', visible: true, order: 4, expanded: false },
+      crypto: { label: 'Crypto', color: 'chart-4', cardColor: 'chart-4', visible: true, order: 5, expanded: false },
+    },
+  },
+};
+
+export function useSettings() {
+  const [settings, setSettings] = useState<UserSettingsData>(DEFAULT_SETTINGS);
+  const [loading, setLoading] = useState(true);
+
+  useEffect(() => {
+    getSettings()
+      .then((r) => setSettings(r.data.data))
+      .catch(() => {}) // use defaults on error
+      .finally(() => setLoading(false));
+  }, []);
+
+  const patchSection = useCallback(
+    async (sectionId: string, partial: Partial<SectionSettings>) => {
+      setSettings((prev) => {
+        const updated = {
+          ...prev,
+          dashboard: {
+            ...prev.dashboard,
+            sections: {
+              ...prev.dashboard.sections,
+              [sectionId]: { ...prev.dashboard.sections[sectionId], ...partial },
+            },
+          },
+        };
+        // Fire-and-forget save
+        updateSettings(updated).catch(console.error);
+        return updated;
+      });
+    },
+    []
+  );
+
+  return { settings, loading, patchSection };
+}