feat(clubs): add Club and Member API endpoints with auto-sync

Implement Task 16: Club + Member API endpoints with MemberSyncService

Services:
- ClubService: GetMyClubsAsync (user's clubs), GetCurrentClubAsync (tenant club)
- MemberService: GetMembersAsync (list), GetMemberByIdAsync, GetCurrentMemberAsync
- MemberSyncService: Auto-creates Member records from JWT on first request

Middleware:
- MemberSyncMiddleware: Runs after auth, calls MemberSyncService

Endpoints:
- GET /api/clubs/me (list user's clubs)
- GET /api/clubs/current (current tenant's club)
- GET /api/members (list members, RLS filtered)
- GET /api/members/{id} (member detail)
- GET /api/members/me (current user's membership)

Tests: 14 integration tests (6 club + 8 member)
- Club filtering by user membership
- Multi-tenant isolation via RLS
- Member auto-sync on first request
- Cross-tenant access blocked
- Role-based authorization

Build: 0 errors, all tests compile
Pattern: TypedResults, RequireAuthorization policies, TDD approach

backend/WorkClub.Api/Services/ClubService.cs

@@ -0,0 +1,79 @@
+using Microsoft.EntityFrameworkCore;
+using WorkClub.Application.Clubs.DTOs;
+using WorkClub.Application.Interfaces;
+using WorkClub.Infrastructure.Data;
+
+namespace WorkClub.Api.Services;
+
+public class ClubService
+{
+    private readonly AppDbContext _context;
+    private readonly ITenantProvider _tenantProvider;
+    private readonly IHttpContextAccessor _httpContextAccessor;
+
+    public ClubService(
+        AppDbContext context,
+        ITenantProvider tenantProvider,
+        IHttpContextAccessor httpContextAccessor)
+    {
+        _context = context;
+        _tenantProvider = tenantProvider;
+        _httpContextAccessor = httpContextAccessor;
+    }
+
+    public async Task<List<ClubListDto>> GetMyClubsAsync()
+    {
+        var userIdClaim = _httpContextAccessor.HttpContext?.User.FindFirst("sub")?.Value;
+        if (string.IsNullOrEmpty(userIdClaim))
+        {
+            return new List<ClubListDto>();
+        }
+
+        var memberships = await _context.Members
+            .Where(m => m.ExternalUserId == userIdClaim)
+            .ToListAsync();
+
+        var clubIds = memberships.Select(m => m.ClubId).ToList();
+
+        var clubs = await _context.Clubs
+            .Where(c => clubIds.Contains(c.Id))
+            .ToListAsync();
+
+        var clubDtos = new List<ClubListDto>();
+        foreach (var club in clubs)
+        {
+            var memberCount = await _context.Members
+                .Where(m => m.ClubId == club.Id)
+                .CountAsync();
+
+            clubDtos.Add(new ClubListDto(
+                club.Id,
+                club.Name,
+                club.SportType.ToString(),
+                memberCount
+            ));
+        }
+
+        return clubDtos;
+    }
+
+    public async Task<ClubDetailDto?> GetCurrentClubAsync()
+    {
+        var tenantId = _tenantProvider.GetTenantId();
+
+        var club = await _context.Clubs
+            .FirstOrDefaultAsync(c => c.TenantId == tenantId);
+
+        if (club == null)
+            return null;
+
+        return new ClubDetailDto(
+            club.Id,
+            club.Name,
+            club.SportType.ToString(),
+            club.Description,
+            club.CreatedAt,
+            club.UpdatedAt
+        );
+    }
+}