Add accounts expansion, analytics, exchange rates, API tokens, PWA support, and UI overhaul

- Expand Account model with account_type (pension, savings, liability, crypto), new banks/currencies (BTC, XMR, FCL, ROP, VOL, MEMP, MPAT, MORTGAGE), and next_payment field
- Add exchange rate endpoint (BCCR integration), analytics endpoint, paste-import for transactions, and API token management
- Add PWA manifest, service worker, and app icons
- Redesign dashboard, transactions, transfers, and login pages with theme support
- Add billing cycle selector, confirm dialog, and paste import modal components
- One-time DB reset in deploy workflow for schema migration

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

frontend/src/ThemeContext.tsx

@@ -0,0 +1,31 @@
+import { createContext, useContext, useEffect, useState } from 'react';
+
+type Theme = 'light' | 'dark';
+
+const ThemeContext = createContext<{
+  theme: Theme;
+  toggleTheme: () => void;
+}>({ theme: 'dark', toggleTheme: () => {} });
+
+export function ThemeProvider({ children }: { children: React.ReactNode }) {
+  const [theme, setTheme] = useState<Theme>(() => {
+    const saved = localStorage.getItem('theme') as Theme;
+    if (saved) return saved;
+    return window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light';
+  });
+
+  useEffect(() => {
+    document.documentElement.classList.toggle('dark', theme === 'dark');
+    localStorage.setItem('theme', theme);
+  }, [theme]);
+
+  const toggleTheme = () => setTheme((t) => (t === 'dark' ? 'light' : 'dark'));
+
+  return (
+    <ThemeContext.Provider value={{ theme, toggleTheme }}>
+      {children}
+    </ThemeContext.Provider>
+  );
+}
+
+export const useTheme = () => useContext(ThemeContext);