feat: add data explorer to sidebar navigation and fix gitignore

- Add "데이터 탐색" menu item to sidebar with Search icon
- Add "수집 데이터 조회" link button on data management page
- Fix sidebar active state to correctly distinguish /admin/data
  from /admin/data/explorer
- Add page title mapping for data explorer in header
- Fix .gitignore: add negation for frontend/src/app/admin/data/
  so admin data pages are tracked without needing git add -f
- Fix dashboard loading state (return null → skeleton with layout)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitignore

@@ -55,6 +55,7 @@ Thumbs.db
 *.db
 *.sqlite3
 data/
+!frontend/src/app/admin/data/
 
 # Test
 .coverage

frontend/src/app/admin/data/page.tsx

@@ -2,6 +2,7 @@
 
 import { useEffect, useState, useRef, useCallback } from 'react';
 import { useRouter } from 'next/navigation';
+import Link from 'next/link';
 import { DashboardLayout } from '@/components/layout/dashboard-layout';
 import { Card, CardContent, CardHeader, CardTitle } from '@/components/ui/card';
 import { Button } from '@/components/ui/button';
@@ -135,7 +136,12 @@ export default function DataManagementPage() {
 
   return (
     <DashboardLayout>
-      <h1 className="text-2xl font-bold text-foreground mb-6">데이터 수집 관리</h1>
+      <div className="flex items-center justify-between mb-6">
+        <h1 className="text-2xl font-bold text-foreground">데이터 수집 관리</h1>
+        <Button asChild variant="outline">
+          <Link href="/admin/data/explorer">수집 데이터 조회</Link>
+        </Button>
+      </div>
 
       {error && (
         <div className="bg-destructive/10 border border-destructive text-destructive px-4 py-3 rounded mb-4">

frontend/src/app/page.tsx

@@ -84,7 +84,26 @@ export default function DashboardPage() {
   }, [router]);
 
   if (loading) {
-    return null; // DashboardLayout handles skeleton
+    return (
+      <DashboardLayout>
+        <div className="space-y-6">
+          <div className="grid gap-4 md:grid-cols-2 lg:grid-cols-4">
+            {Array.from({ length: 4 }).map((_, i) => (
+              <Card key={i}>
+                <CardContent className="pt-6">
+                  <div className="h-4 w-20 bg-muted animate-pulse rounded mb-2" />
+                  <div className="h-8 w-32 bg-muted animate-pulse rounded" />
+                </CardContent>
+              </Card>
+            ))}
+          </div>
+          <div className="grid gap-4 md:grid-cols-2">
+            <Card><CardContent className="pt-6"><div className="h-64 bg-muted animate-pulse rounded" /></CardContent></Card>
+            <Card><CardContent className="pt-6"><div className="h-64 bg-muted animate-pulse rounded" /></CardContent></Card>
+          </div>
+        </div>
+      </DashboardLayout>
+    );
   }
 
   const totalValue = portfolios.reduce((sum, p) => sum + (p.total_value ?? 0), 0);

frontend/src/components/layout/new-header.tsx

@@ -10,7 +10,8 @@ const pageTitles: Record<string, string> = {
   '/portfolio': '포트폴리오',
   '/strategy': '전략',
   '/backtest': '백테스트',
-  '/admin/data': '데이터 관리',
+  '/admin/data': '데이터 수집',
+  '/admin/data/explorer': '데이터 탐색',
 };
 
 function getPageTitle(pathname: string): string {
@@ -19,12 +20,16 @@ function getPageTitle(pathname: string): string {
     return pageTitles[pathname];
   }
 
-  // Check for partial matches (for nested routes)
+  // Check for partial matches (for nested routes), prefer longest match
+  let bestMatch = '';
+  let bestTitle = '';
   for (const [path, title] of Object.entries(pageTitles)) {
-    if (path !== '/' && pathname.startsWith(path)) {
-      return title;
+    if (path !== '/' && pathname.startsWith(path) && path.length > bestMatch.length) {
+      bestMatch = path;
+      bestTitle = title;
     }
   }
+  if (bestTitle) return bestTitle;
 
   return '대시보드';
 }

frontend/src/components/layout/new-sidebar.tsx

@@ -9,6 +9,7 @@ import {
   TrendingUp,
   FlaskConical,
   Database,
+  Search,
   ChevronLeft,
   ChevronRight,
 } from 'lucide-react';
@@ -27,7 +28,8 @@ const navItems = [
   { href: '/portfolio', label: '포트폴리오', icon: Briefcase },
   { href: '/strategy', label: '전략', icon: TrendingUp },
   { href: '/backtest', label: '백테스트', icon: FlaskConical },
-  { href: '/admin/data', label: '데이터 관리', icon: Database },
+  { href: '/admin/data', label: '데이터 수집', icon: Database },
+  { href: '/admin/data/explorer', label: '데이터 탐색', icon: Search },
 ];
 
 interface NewSidebarProps {
@@ -84,7 +86,8 @@ export function NewSidebar({ collapsed = false, onCollapsedChange }: NewSidebarP
             {navItems.map((item) => {
               const isActive =
                 pathname === item.href ||
-                (item.href !== '/' && pathname.startsWith(item.href));
+                (item.href !== '/' && pathname.startsWith(item.href) &&
+                  !navItems.some((other) => other.href !== item.href && other.href.startsWith(item.href) && pathname.startsWith(other.href)));
               const Icon = item.icon;
 
               const linkContent = (