Fix DbContext concurrency error in parallel company verification

Use IDbContextFactory pattern to create isolated DbContext instances
for each cache operation, making parallel verification thread-safe.

Changes:
- Add IDbContextFactory<ApplicationDbContext> registration
- Update CompanyVerifierService to use factory for cache operations
- Update tests with InMemoryDatabaseRoot for shared test data

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

src/TrueCV.Infrastructure/DependencyInjection.cs

@@ -19,6 +19,19 @@ public static class DependencyInjection
     public static IServiceCollection AddInfrastructure(this IServiceCollection services, IConfiguration configuration)
     {
         // Configure DbContext with SQL Server
+        // AddDbContextFactory enables thread-safe parallel operations
+        services.AddDbContextFactory<ApplicationDbContext>(options =>
+            options.UseSqlServer(
+                configuration.GetConnectionString("DefaultConnection"),
+                sqlOptions =>
+                {
+                    sqlOptions.EnableRetryOnFailure(
+                        maxRetryCount: 3,
+                        maxRetryDelay: TimeSpan.FromSeconds(30),
+                        errorNumbersToAdd: null);
+                }));
+
+        // Also register DbContext for scoped injection (non-parallel scenarios)
         services.AddDbContext<ApplicationDbContext>(options =>
             options.UseSqlServer(
                 configuration.GetConnectionString("DefaultConnection"),