Refactor nunit tests off InMemory/WebApplicationFactory, remove tuple returns (#4)

## Summary
- Extract `IMicCheckDbContext` and mock DB access with Moq instead of the EF InMemory provider, per CLAUDE.md testing guidelines.
- Rewrite HTTP-pipeline tests to exercise controllers/auth handlers directly instead of `WebApplicationFactory`.
- Remove tuple return types across the API in favor of named records (`PagedResult<T>`, `ProfileUpdateResult`, `ApiKeyCreationResult`).

## Test plan
- [x] `dotnet build` (full solution)
- [x] `dotnet test tests/api/MicCheck.Api.Tests.Unit` — 187/187 pass
- [x] `dotnet test tests/api/MicCheck.Api.Tests.Integration` — 8/8 pass (live API + Postgres via Aspire)
- [x] Verified Aspire AppHost/dashboard starts and API responds

Reviewed-on: #4

src/api/MicCheck.Api/Audit/AuditLogQueryService.cs

@@ -1,32 +1,33 @@
+using MicCheck.Api.Common;
 using MicCheck.Api.Data;
 using Microsoft.EntityFrameworkCore;
 
 namespace MicCheck.Api.Audit;
 
-public class AuditLogQueryService(MicCheckDbContext db)
+public class AuditLogQueryService(IMicCheckDbContext db)
 {
-    public async Task<(int Total, IReadOnlyList<AuditLogResponse> Items)> ListByOrganizationAsync(
+    public async Task<PagedResult<AuditLogResponse>> ListByOrganizationAsync(
         int organizationId, AuditLogFilter filter, CancellationToken ct = default)
     {
         var query = db.AuditLogs.Where(l => l.OrganizationId == organizationId);
         return await ApplyFilterAndPageAsync(query, filter, ct);
     }
 
-    public async Task<(int Total, IReadOnlyList<AuditLogResponse> Items)> ListByProjectAsync(
+    public async Task<PagedResult<AuditLogResponse>> ListByProjectAsync(
         int projectId, AuditLogFilter filter, CancellationToken ct = default)
     {
         var query = db.AuditLogs.Where(l => l.ProjectId == projectId);
         return await ApplyFilterAndPageAsync(query, filter, ct);
     }
 
-    public async Task<(int Total, IReadOnlyList<AuditLogResponse> Items)> ListByEnvironmentAsync(
+    public async Task<PagedResult<AuditLogResponse>> ListByEnvironmentAsync(
         int environmentId, AuditLogFilter filter, CancellationToken ct = default)
     {
         var query = db.AuditLogs.Where(l => l.EnvironmentId == environmentId);
         return await ApplyFilterAndPageAsync(query, filter, ct);
     }
 
-    private async Task<(int Total, IReadOnlyList<AuditLogResponse> Items)> ApplyFilterAndPageAsync(
+    private async Task<PagedResult<AuditLogResponse>> ApplyFilterAndPageAsync(
         IQueryable<AuditLog> query, AuditLogFilter filter, CancellationToken ct)
     {
         if (filter.From.HasValue)
@@ -63,6 +64,6 @@ public class AuditLogQueryService(MicCheckDbContext db)
                     user != null ? user.FirstName + " " + user.LastName : null))
             .ToListAsync(ct);
 
-        return (total, items);
+        return new PagedResult<AuditLogResponse>(total, items);
     }
 }