Moscow-time date display, CSRF error UX, session cookie hardening

- DateUtils: format ISO instants as dd.MM.yyyy HH:mm in Europe/Moscow
- admin/lab page and student dashboard show deadlines in MSK time
- CSRF failure redirects to /login with friendly message instead of 403
- session tracking-modes=cookie (no ;jsessionid in URLs) (previously set)
- web rebuild with all dialog/status-toggle fixes verified end-to-end

web/src/main/kotlin/ru/ysu/lms/web/DateUtils.kt

@@ -0,0 +1,21 @@
+package ru.ysu.lms.web
+
+import java.time.Instant
+import java.time.ZoneId
+import java.time.ZonedDateTime
+import java.time.format.DateTimeFormatter
+
+object DateUtils {
+    private val MSK = ZoneId.of("Europe/Moscow")
+    private val FORMAT = DateTimeFormatter.ofPattern("dd.MM.yyyy HH:mm")
+
+    fun formatMsk(value: String?): String? =
+        value?.let {
+            try {
+                val zdt = ZonedDateTime.ofInstant(Instant.parse(it), MSK)
+                zdt.format(FORMAT)
+            } catch (_: Exception) {
+                it
+            }
+        }
+}

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

@@ -283,6 +283,8 @@ class AdminController(
         model.addAttribute("lab", lab)
         model.addAttribute("groups", groupSections)
         model.addAttribute("descriptionHtml", markdown.render(lab.descriptionMd))
+        model.addAttribute("deadlineMsk", ru.ysu.lms.web.DateUtils.formatMsk(lab.deadlineAt))
+        model.addAttribute("defenseMsk", ru.ysu.lms.web.DateUtils.formatMsk(lab.defenseAt))
         model.addAttribute("deadlineLocal", lab.deadlineAt?.take(16) ?: "")
         model.addAttribute("defenseLocal", lab.defenseAt?.take(16) ?: "")
         return "admin/lab"

web/src/main/kotlin/ru/ysu/lms/web/api/ApiDtos.kt

@@ -153,6 +153,8 @@ data class MeAssignmentDto(
     val pointsMax: Any? = null,
 ) {
     var statementHtml: String = ""
+    var deadlineMsk: String? = null
+    var defenseMsk: String? = null
 }
 
 @JsonIgnoreProperties(ignoreUnknown = true)

web/src/main/kotlin/ru/ysu/lms/web/auth/AuthPageController.kt

@@ -27,6 +27,10 @@ class AuthPageController(private val api: ApiClient) {
         if (currentUser(session) != null) {
             return "redirect:/"
         }
+        (session.getAttribute("csrfError") as? String)?.let {
+            session.removeAttribute("csrfError")
+            model.addAttribute("error", it)
+        }
         model.addAttribute("adminExists", api.adminExists())
         return "login"
     }

web/src/main/kotlin/ru/ysu/lms/web/config/CsrfInterceptor.kt

@@ -29,13 +29,26 @@ class CsrfInterceptor : HandlerInterceptor {
         if (request.method.equals("POST", ignoreCase = true)) {
             val sent = request.getParameter(FIELD)
             if (sent != token) {
-                response.sendError(HttpServletResponse.SC_FORBIDDEN, "CSRF token mismatch")
+                request.getSession().setAttribute("csrfError", "CSRF-токен устарел. Попробуйте ещё раз.")
+                response.sendRedirect("/login")
                 return false
             }
         }
         return true
     }
 
+    override fun afterCompletion(
+        request: HttpServletRequest,
+        response: HttpServletResponse,
+        handler: Any,
+        ex: Exception?,
+    ) {
+        // после успешного POST-запроса чистим флаг ошибки (если был)
+        if (request.method.equals("POST", ignoreCase = true)) {
+            request.getSession().removeAttribute("csrfError")
+        }
+    }
+
     companion object {
         const val ATTR = "csrfToken"
         const val FIELD = "_csrf"

web/src/main/kotlin/ru/ysu/lms/web/student/StudentController.kt

@@ -21,7 +21,11 @@ class StudentController(
     fun dashboard(session: HttpSession, model: Model): String {
         val token = session.getAttribute(SessionKeys.TOKEN) as? String ?: return "redirect:/login"
         val assignments = api.meAssignments(token).map {
-            it.apply { statementHtml = markdown.render(statementMd) }
+            it.apply {
+                statementHtml = markdown.render(statementMd)
+                deadlineMsk = ru.ysu.lms.web.DateUtils.formatMsk(deadlineAt)
+                defenseMsk = ru.ysu.lms.web.DateUtils.formatMsk(defenseAt)
+            }
         }
         model.addAttribute("assignments", assignments)
         return "student/dashboard"

web/src/main/resources/application.yml

@@ -5,6 +5,7 @@ server:
       cookie:
         http-only: true
         same-site: lax
+      tracking-modes: cookie
 
 spring:
   application:

web/src/main/resources/templates/admin/lab.html

@@ -13,8 +13,8 @@
                     <input type="hidden" name="_csrf" th:value="${csrfToken}">
                     <button class="btn btn-secondary btn-sm ml-2" onclick="return confirm('Сменить статус лабораторной?')" type="submit">Сменить статус</button>
                 </form>
-                <span th:if="${lab.deadlineAt != null}"> · Срок: <span th:text="${lab.deadlineAt}"></span></span>
+                <span th:if="${deadlineMsk != null}"> · Срок: <span th:text="${deadlineMsk} + ' МСК'"></span></span>
-                <span th:if="${lab.defenseAt != null}"> · Защита: <span th:text="${lab.defenseAt}"></span></span>
+                <span th:if="${defenseMsk != null}"> · Защита: <span th:text="${defenseMsk} + ' МСК'"></span></span>
                 · Максимум: <span th:text="${lab.pointsMax}"></span> б.
             </p>
         </div>

web/src/main/resources/templates/student/dashboard.html

@@ -20,8 +20,8 @@
                 </div>
             </div>
             <p class="text-sm text-muted" th:if="${a.variantTitle}" th:text="${a.variantTitle}">—</p>
-            <p class="text-sm text-muted" th:if="${a.deadlineAt}" th:text="|Срок сдачи: ${a.deadlineAt}|">—</p>
+            <p class="text-sm text-muted" th:if="${a.deadlineMsk}" th:text="|Срок сдачи: ${a.deadlineMsk} (МСК)|">—</p>
-            <p class="text-sm text-muted" th:if="${a.defenseAt}" th:text="|Защита: ${a.defenseAt}|">—</p>
+            <p class="text-sm text-muted" th:if="${a.defenseMsk}" th:text="|Защита: ${a.defenseMsk} (МСК)|">—</p>
             <div class="md-body mt-4" th:utext="${a.statementHtml}"></div>
         </div>
     </div>