fix(cv): support application variant deep links

The Application Workspace CV section linked to /cv-builder?variant={id}. That
route does not exist: the builder is mounted at /career/builder/:id and reads the
variant from the path, not a query string. The button dead-ended.

Corrected the href. No loading logic was added — the editor already loads the
variant by id and already has a safe error state, and ownership is already
enforced server-side, where CvVariantService scopes every read to the owner and
the controller returns 404.

Added tests for the deep-link entry point, which had none: the variant loads from
the route, a missing variant shows the error state rather than an empty editor,
and another user's variant is refused identically. The asset test now asserts the
exact href, so a route that the router does not serve fails the build instead of
shipping.

118 frontend tests and the production build pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

job-tracker-ui/src/application-assets.test.tsx

@@ -74,8 +74,10 @@ test("cv section shows the attached variant and the ones available to attach", a
 
   expect(await screen.findByText("Backend CV")).toBeInTheDocument();
   expect(screen.getByText(/Theme nordic · version 4/)).toBeInTheDocument();
+  // Must be the builder's real route (/career/builder/:id). An href the router does not serve
+  // silently dead-ends the user, which is exactly what shipped before this test existed.
   expect(screen.getByRole("link", { name: /Edit, preview and export/i })).toHaveAttribute(
-    "href", "/cv-builder?variant=3");
+    "href", "/career/builder/3");
 });
 
 test("attaching a different variant only re-points the application", async () => {