feat: complete release readiness work

- consolidate API ownership and remove dead vendor code

- add Stripe billing, learning paths, and public CV hardening

- add migration, recovery, security, audit, and browser gates

JobTrackerApi.Tests/JobApplicationsEndpointBehaviorTests.cs

@@ -209,6 +209,8 @@ public sealed class JobApplicationsEndpointBehaviorTests
         var result = await controller.Create(request, CancellationToken.None);
 
         Assert.NotNull(result);
+        var created = Assert.IsType<CreatedAtActionResult>(result.Result);
+        Assert.IsType<JobApplicationDto>(created.Value);
         var saved = await db.JobApplications.FirstAsync();
         Assert.Equal(60000m, saved.SalaryMin);
         Assert.Equal(70000m, saved.SalaryMax);