fix(web): устойчивые ошибки courseNo и login E2E

web/src/main/kotlin/ru/ysu/lms/web/admin/AdminLabController.kt

@@ -61,7 +61,12 @@ class AdminLabController(
         model: Model,
     ): String {
         val t = token(session)
-        val selected = courseNo?.trim()?.takeIf { it.isNotBlank() }?.let { api.courseByUrlNo(t, it) }
+        val selected =
+            courseNo?.trim()?.takeIf { it.isNotBlank() }?.let {
+                runCatching { api.courseByUrlNo(t, it) }
+                    .onFailure { model.addAttribute("error", "Курс не найден") }
+                    .getOrNull()
+            }
         model.addAttribute("labs", api.listLabs(t, selected?.id))
         model.addAttribute("courses", coursesFor(session))
         model.addAttribute("selectedCourseNo", selected?.courseNo)

web/src/main/kotlin/ru/ysu/lms/web/teacher/TeacherController.kt

@@ -92,7 +92,13 @@ class TeacherController(
         redirect: RedirectAttributes,
     ): String {
         val token = token(session) ?: return "redirect:/login"
-        val course = api.courseByUrlNo(token, courseNo)
+        val course =
+            try {
+                api.courseByUrlNo(token, courseNo)
+            } catch (ex: ApiException) {
+                redirect.addFlashAttribute("error", ex.message)
+                return "redirect:/teacher"
+            }
         return try {
             val target = groupId.trim().ifBlank { throw ApiException(400, "Выберите группу") }
             api.attachCourseGroup(token, course.id, CourseGroupPayload(target))
@@ -112,7 +118,13 @@ class TeacherController(
         redirect: RedirectAttributes,
     ): String {
         val token = token(session) ?: return "redirect:/login"
-        val course = api.courseByUrlNo(token, courseNo)
+        val course =
+            try {
+                api.courseByUrlNo(token, courseNo)
+            } catch (ex: ApiException) {
+                redirect.addFlashAttribute("error", ex.message)
+                return "redirect:/teacher"
+            }
         return try {
             api.detachCourseGroup(token, course.id, groupId)
             redirect.addFlashAttribute("notice", "Группа отвязана от курса")