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>

src/TaxBaik.Web.Client/Services/ClientBrowserClient.cs

@@ -0,0 +1,141 @@
+namespace TaxBaik.Web.Services;
+
+using System.Net.Http;
+using System.Net.Http.Json;
+using TaxBaik.Application.DTOs;
+using TaxBaik.Domain.Entities;
+
+/// <summary>
+/// Client API Client for Admin Blazor
+/// SOLID: Single Responsibility - Client API calls only
+/// </summary>
+public interface IClientBrowserClient
+{
+    Task<(IEnumerable<Client> Items, int Total)> GetPagedAsync(
+        int page = 1, int pageSize = 20, string? status = null, string? search = null, CancellationToken ct = default);
+    Task<Client?> GetByIdAsync(int id, CancellationToken ct = default);
+    Task<Client?> CreateAsync(CreateClientDto dto, CancellationToken ct = default);
+    Task<Client?> UpdateAsync(int id, CreateClientDto dto, CancellationToken ct = default);
+    Task<bool> DeleteAsync(int id, CancellationToken ct = default);
+}
+
+public class ClientBrowserClient : IClientBrowserClient
+{
+    private readonly HttpClient _http;
+    private readonly ILogger<ClientBrowserClient> _logger;
+    private readonly ITokenStore _tokenStore;
+
+    public ClientBrowserClient(HttpClient http, ILogger<ClientBrowserClient> logger, ITokenStore tokenStore)
+    {
+        _http = http;
+        _logger = logger;
+        _tokenStore = tokenStore;
+    }
+
+    private void EnsureAuthHeader()
+    {
+        if (!string.IsNullOrEmpty(_tokenStore.AccessToken))
+            _http.DefaultRequestHeaders.Authorization = new("Bearer", _tokenStore.AccessToken);
+        else
+            _http.DefaultRequestHeaders.Authorization = null;
+    }
+
+    public async Task<(IEnumerable<Client> Items, int Total)> GetPagedAsync(
+        int page = 1, int pageSize = 20, string? status = null, string? search = null, CancellationToken ct = default)
+    {
+        try
+        {
+            EnsureAuthHeader();
+            var query = $"client?page={page}&pageSize={pageSize}";
+            if (!string.IsNullOrEmpty(status))
+                query += $"&status={status}";
+            if (!string.IsNullOrEmpty(search))
+                query += $"&search={Uri.EscapeDataString(search)}";
+
+            var result = await _http.GetFromJsonAsync<ClientPagedResponse>(query, cancellationToken: ct);
+            return result != null ? (result.Data, result.Total) : ([], 0);
+        }
+        catch (HttpRequestException ex)
+        {
+            _logger.LogError(ex, "Failed to fetch clients");
+            throw;
+        }
+    }
+
+    public async Task<Client?> GetByIdAsync(int id, CancellationToken ct = default)
+    {
+        try
+        {
+            EnsureAuthHeader();
+            return await _http.GetFromJsonAsync<Client>($"client/{id}", cancellationToken: ct);
+        }
+        catch (HttpRequestException ex)
+        {
+            _logger.LogError(ex, "Failed to fetch client {ClientId}", id);
+            throw;
+        }
+    }
+
+    public async Task<Client?> CreateAsync(CreateClientDto dto, CancellationToken ct = default)
+    {
+        try
+        {
+            EnsureAuthHeader();
+            var response = await _http.PostAsJsonAsync("client", dto, cancellationToken: ct);
+            if (!response.IsSuccessStatusCode)
+                return null;
+
+            var content = await response.Content.ReadAsStringAsync(ct);
+            return System.Text.Json.JsonSerializer.Deserialize<Client>(
+                content,
+                new System.Text.Json.JsonSerializerOptions { PropertyNameCaseInsensitive = true });
+        }
+        catch (HttpRequestException ex)
+        {
+            _logger.LogError(ex, "Failed to create client");
+            throw;
+        }
+    }
+
+    public async Task<Client?> UpdateAsync(int id, CreateClientDto dto, CancellationToken ct = default)
+    {
+        try
+        {
+            EnsureAuthHeader();
+            var response = await _http.PutAsJsonAsync($"client/{id}", dto, cancellationToken: ct);
+            if (!response.IsSuccessStatusCode)
+                return null;
+
+            var content = await response.Content.ReadAsStringAsync(ct);
+            return System.Text.Json.JsonSerializer.Deserialize<Client>(
+                content,
+                new System.Text.Json.JsonSerializerOptions { PropertyNameCaseInsensitive = true });
+        }
+        catch (HttpRequestException ex)
+        {
+            _logger.LogError(ex, "Failed to update client {ClientId}", id);
+            throw;
+        }
+    }
+
+    public async Task<bool> DeleteAsync(int id, CancellationToken ct = default)
+    {
+        try
+        {
+            EnsureAuthHeader();
+            var response = await _http.DeleteAsync($"client/{id}", cancellationToken: ct);
+            return response.IsSuccessStatusCode;
+        }
+        catch (HttpRequestException ex)
+        {
+            _logger.LogError(ex, "Failed to delete client {ClientId}", id);
+            throw;
+        }
+    }
+
+    private class ClientPagedResponse
+    {
+        public List<Client> Data { get; set; } = [];
+        public int Total { get; set; }
+    }
+}