fix: remove [Authorize] from Dashboard, add internal auth check

Root cause: [Authorize] attribute was blocking /dashboard access before
Blazor auth state could be established, causing redirect to /not-found.

Solution:
- Remove [Authorize] from Dashboard.razor
- Add authentication check in OnInitializedAsync
- If not authenticated, redirect to login internally
- Reduced wait time from 6s to 3s in login.html

This allows:
1. /dashboard to load immediately
2. Blazor auth state to initialize
3. Dashboard to verify user is authenticated
4. Redirect to login if not authenticated

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

test-no-cache.mjs

@@ -0,0 +1,58 @@
+import { chromium } from "@playwright/test";
+
+(async () => {
+  console.log("=== TEST WITH CACHE BYPASS ===\n");
+  
+  const b = await chromium.launch({ headless: false });
+  const ctx = await b.createIncognitoBrowserContext(); // Private mode = no cache
+  const p = await ctx.newPage();
+  
+  p.on("console", msg => {
+    if (msg.text().includes("[Login]")) {
+      console.log(`  ✓ ${msg.text()}`);
+    }
+  });
+  
+  try {
+    // 캐시 무시하고 로드
+    console.log("1. Loading login page (no cache)...");
+    await p.goto("http://localhost:5265/login.html?nocache=" + Date.now(), { 
+      waitUntil: "networkidle" 
+    });
+    console.log("   ✓ Loaded\n");
+    
+    console.log("2. Submitting login...");
+    await p.fill("input[name='username']", "admin");
+    await p.fill("input[name='password']", "admin");
+    await p.click("button[type='submit']");
+    console.log("   ✓ Submitted\n");
+    
+    console.log("3. Waiting 8 seconds...");
+    for (let i = 1; i <= 8; i++) {
+      await new Promise(r => setTimeout(r, 1000));
+      const url = p.url();
+      process.stdout.write(`   [${i}s] ${url}\r`);
+    }
+    
+    console.log("\n\n4. FINAL CHECK:");
+    const finalUrl = p.url();
+    if (finalUrl.includes("/dashboard")) {
+      console.log("   ✓✓✓ SUCCESS: Dashboard loaded!");
+      const content = await p.content();
+      if (content.includes("관리자 대시보드")) {
+        console.log("   ✓ Dashboard content confirmed!");
+      }
+    } else if (finalUrl.includes("/not-found")) {
+      console.log("   ✗ /not-found (auth failed)");
+    } else {
+      console.log("   URL: " + finalUrl);
+    }
+    
+    await p.screenshot({ path: "./final-test-no-cache.png", fullPage: true });
+    
+  } catch (e) {
+    console.error("Error:", e.message);
+  } finally {
+    await b.close();
+  }
+})();