fix: resolve all 47 noctx lint findings in tests

Replace every httptest.NewRequest call with
httptest.NewRequestWithContext using the test's t.Context(). Thread
t *testing.T through the createSetupFormRequest and
createLoginFormRequest helpers so they can supply a context.

make lint under golangci-lint 2.12.2 drops from 94 findings to 47
(remaining: 23 gosec, 24 goconst, tracked in #176/#177/#178). make
test and make fmt-check pass unchanged.

Closes #175

internal/service/auth/auth_test.go

@@ -121,7 +121,7 @@ func getSessionCookie(t *testing.T, svc *auth.Service) *http.Cookie {
 	require.NoError(t, err)
 
 	recorder := httptest.NewRecorder()
-	request := httptest.NewRequest(http.MethodGet, "/", nil)
+	request := httptest.NewRequestWithContext(t.Context(), http.MethodGet, "/", nil)
 
 	err = svc.CreateSession(recorder, request, user)
 	require.NoError(t, err)
@@ -380,7 +380,7 @@ func TestDestroySessionMaxAge(testingT *testing.T) {
 		defer cleanup()
 
 		recorder := httptest.NewRecorder()
-		request := httptest.NewRequest(http.MethodGet, "/", nil)
+		request := httptest.NewRequestWithContext(t.Context(), http.MethodGet, "/", nil)
 
 		err := svc.DestroySession(recorder, request)
 		require.NoError(t, err)