Initial commit: LMS microservices scaffold

- Gradle multi-module: libs/{common-http,security-jwt,markdown,test-support},
  services/{identity,academic,progress,gateway}, web (Thymeleaf+htmx)
- identity-service: JWT auth (RSA), accounts, students, groups, enrollment,
  import from XLSX/CSV, credentials export, password reset
- academic-service: lab import from JSON/zip (markdown + YAML + variants),
  levels, API
- progress-service: schema for student levels and variant assignments
- gateway: Spring Cloud Gateway, JWT validation, route propagation
- web: Server-side UI with flex/footer layout, light/dark theme toggle,
  admin dashboard, groups CRUD, student portal placeholder
- docker-compose: PostgreSQL 18
- Tests: identity smoke test with Testcontainers

web/src/main/resources/templates/error.html

@@ -0,0 +1,14 @@
+<!DOCTYPE html>
+<html lang="ru" xmlns:th="http://www.thymeleaf.org"
+      th:replace="~{fragments/base :: layout(~{::title}, ~{::#content})}">
+<head><title>Ошибка — LMS</title></head>
+<body>
+<div id="content">
+    <div style="max-width:28rem;margin:0 auto;text-align:center;">
+        <p style="font-size:4rem;font-weight:700;color:var(--c-text-muted);opacity:0.3;" th:text="${status}">500</p>
+        <p style="margin-top:1rem;" th:text="${message}">Что-то пошло не так</p>
+        <a class="btn btn-secondary" style="margin-top:1.5rem;display:inline-flex;" th:href="@{/}">На главную</a>
+    </div>
+</div>
+</body>
+</html>