feat: standalone Blazor WebAssembly admin + SEO enhancements

Architecture:
- Admin UI: /admin (Standalone Blazor WebAssembly, 219 WASM files)
- Portal: /portal (Razor Pages, Cookie/OAuth auth)
- Homepage: / (Razor Pages, SSR)
- API: /api (FastEndpoints + JWT)

SEO:
- Sitemap: Public content only (blog, FAQ, announcements, contact)
- robots.txt: Exclude /admin and /portal, reference production domain
- Naver verification: naverb1813cd79ddc2ded5c5291fca5cb46c2.html ready

Technical:
- TaxBaik.Web.Client: StaticWebAssetBasePath=admin
- Server Program.cs: UseBlazorFrameworkFiles + MapFallback for SPA routing
- base href="/admin/" for client-side navigation
- blazor.webassembly.js (standalone, not web.js)

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

tmp/naverb1813cd79ddc2ded5c5291fca5cb46c2.html

@@ -0,0 +1 @@
+naver-site-verification: naverb1813cd79ddc2ded5c5291fca5cb46c2.html