refactor: restructure project directories for better modularity

- Delete llm/ dead code (3 files, zero references)
- Split mcp/ into sub-packages: mcp/provider/ (8 providers) and
  mcp/payment/ (4 payment clients) with registry pattern
- Export Client internal fields and ClientHooks interface for
  sub-package access
- Split api/server.go (3892 lines) into 8 domain-specific handler files
- Split trader/auto_trader.go (2296 lines) into 5 focused files
- Reorganize web/src/components/ flat files into auth/, charts/,
  trader/, common/, modals/, backtest/ subdirectories
- Update all consumer imports to use registry-based provider creation

web/src/components/common/Header.tsx

@@ -0,0 +1,76 @@
+import { useLanguage } from '../../contexts/LanguageContext'
+import { t } from '../../i18n/translations'
+import { Container } from './Container'
+
+interface HeaderProps {
+  simple?: boolean // For login/register pages
+}
+
+export function Header({ simple = false }: HeaderProps) {
+  const { language, setLanguage } = useLanguage()
+
+  return (
+    <header className="glass sticky top-0 z-50 backdrop-blur-xl">
+      <Container className="py-4">
+        <div className="flex items-center justify-between">
+          {/* Left - Logo and Title */}
+          <div className="flex items-center gap-3">
+            <div className="flex items-center justify-center">
+              <img src="/icons/nofx.svg" alt="NoFx Logo" className="w-8 h-8" />
+            </div>
+            <div>
+              <h1 className="text-xl font-bold" style={{ color: '#EAECEF' }}>
+                {t('appTitle', language)}
+              </h1>
+              {!simple && (
+                <p className="text-xs mono" style={{ color: '#848E9C' }}>
+                  {t('subtitle', language)}
+                </p>
+              )}
+            </div>
+          </div>
+
+          {/* Right - Language Toggle (always show) */}
+          <div
+            className="flex gap-1 rounded p-1"
+            style={{ background: '#1E2329' }}
+          >
+            <button
+              onClick={() => setLanguage('zh')}
+              className="px-3 py-1.5 rounded text-xs font-semibold transition-all"
+              style={
+                language === 'zh'
+                  ? { background: '#F0B90B', color: '#000' }
+                  : { background: 'transparent', color: '#848E9C' }
+              }
+            >
+              中文
+            </button>
+            <button
+              onClick={() => setLanguage('en')}
+              className="px-3 py-1.5 rounded text-xs font-semibold transition-all"
+              style={
+                language === 'en'
+                  ? { background: '#F0B90B', color: '#000' }
+                  : { background: 'transparent', color: '#848E9C' }
+              }
+            >
+              EN
+            </button>
+            <button
+              onClick={() => setLanguage('id')}
+              className="px-3 py-1.5 rounded text-xs font-semibold transition-all"
+              style={
+                language === 'id'
+                  ? { background: '#F0B90B', color: '#000' }
+                  : { background: 'transparent', color: '#848E9C' }
+              }
+            >
+              ID
+            </button>
+          </div>
+        </div>
+      </Container>
+    </header>
+  )
+}