refactor: Phase 7-3 - Clients + TaxFilings API-First (WIP)

**Clients Migration Complete:**
- ClientController: GET /api/client (paged), POST/PUT/DELETE
- ClientBrowserClient: IClientBrowserClient interface + implementation
- ClientList.razor: Service → API client
- ClientEdit.razor: Service → API client (Create/Update)

**TaxFilings API Framework Ready:**
- TaxFilingController: GET upcoming, GET by client, POST/PUT/DELETE
- TaxFilingBrowserClient: ITaxFilingBrowserClient interface + impl
- Registered in Program.cs with TokenRefreshHandler

**SOLID Applied:**
✓ Separation of concerns (Controller → Service → Repository)
✓ Dependency inversion (Blazor → Browser clients, not services)
✓ Interface segregation (Specialized clients per domain)

**Status:**
- Clients Blazor: ✅ ClientList + ClientEdit refactored
- TaxFilings Blazor: ⏳ Pending refactor (pages exist)
- Faqs: ⏳ API + Blazor pending
- Announcements: ⏳ API + Blazor pending
- Phase 6 SignalR: ⏳ Deferred

Next: Refactor TaxFilings Blazor pages, then Faqs & Announcements
Build: ✅ Success (0 errors, 2 warnings in Dashboard)

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

TaxBaik.Web/Controllers/ClientController.cs

@@ -0,0 +1,80 @@
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using TaxBaik.Application.DTOs;
+using TaxBaik.Application.Services;
+
+namespace TaxBaik.Web.Controllers;
+
+[ApiController]
+[Route("api/[controller]")]
+[Authorize]
+public class ClientController : ControllerBase
+{
+    private readonly ClientService _clientService;
+
+    public ClientController(ClientService clientService)
+    {
+        _clientService = clientService;
+    }
+
+    [HttpGet]
+    public async Task<IActionResult> GetPaged(
+        [FromQuery] int page = 1,
+        [FromQuery] int pageSize = 20,
+        [FromQuery] string? status = null,
+        [FromQuery] string? search = null)
+    {
+        var (clients, total) = await _clientService.GetPagedAsync(page, pageSize, status, search);
+        return Ok(new { data = clients, total, page, pageSize });
+    }
+
+    [HttpGet("{id}")]
+    public async Task<IActionResult> GetById(int id)
+    {
+        var client = await _clientService.GetByIdAsync(id);
+        if (client == null)
+            return NotFound(new ProblemDetails { Title = "고객을 찾을 수 없습니다.", Status = StatusCodes.Status404NotFound });
+
+        return Ok(client);
+    }
+
+    [HttpPost]
+    public async Task<IActionResult> Create([FromBody] CreateClientDto dto)
+    {
+        try
+        {
+            var clientId = await _clientService.CreateAsync(dto);
+            var client = await _clientService.GetByIdAsync(clientId);
+            return CreatedAtAction(nameof(GetById), new { id = clientId }, client);
+        }
+        catch (ValidationException ex)
+        {
+            return BadRequest(new ProblemDetails { Title = ex.Message, Status = StatusCodes.Status400BadRequest });
+        }
+    }
+
+    [HttpPut("{id}")]
+    public async Task<IActionResult> Update(int id, [FromBody] CreateClientDto dto)
+    {
+        try
+        {
+            await _clientService.UpdateAsync(id, dto);
+            var client = await _clientService.GetByIdAsync(id);
+            if (client == null)
+                return NotFound(new ProblemDetails { Title = "고객을 찾을 수 없습니다.", Status = StatusCodes.Status404NotFound });
+
+            return Ok(client);
+        }
+        catch (ValidationException ex)
+        {
+            return BadRequest(new ProblemDetails { Title = ex.Message, Status = StatusCodes.Status400BadRequest });
+        }
+    }
+
+    [HttpDelete("{id}")]
+    public async Task<IActionResult> Delete(int id)
+    {
+        await _clientService.DeleteAsync(id);
+        return NoContent();
+    }
+}