Content import: sync sections and articles (archive is the source of truth)

- importZip now updates titles/positions of existing chapters and sections and
  removes sections/articles of archived chapters that are missing in the archive
  (so restructured material no longer leaves stale sections behind); removed
  count is reported in ContentImportResult and in the admin flash message
- docs: note about import semantics in the class diagram and sequences

services/academic-service/src/main/kotlin/ru/ysu/lms/academic/content/ContentService.kt

@@ -59,6 +59,8 @@ data class ContentImportResult(
     val sections: Int,
     val articles: Int,
     val assets: Int,
+    /** Сколько устаревших разделов и статей удалено при синхронизации. */
+    val removed: Int = 0,
 )
 
 /**
@@ -453,24 +455,38 @@ class ContentService(
         var chCount = 0
         var secCount = 0
         var artCount = 0
+        var removedCount = 0
         var currentChapter: ContentChapter? = null
         var currentSection: ContentSection? = null
+        val touchedChapters = mutableSetOf<UUID>()
+        val seenSections = mutableSetOf<UUID>()
+        val seenArticles = mutableSetOf<UUID>()
 
         for (p in parsed) {
             if (currentChapter?.title != p.chapterDir) {
                 val slug = chapterSlug(p) ?: "chapter-${chCount + 1}"
-                currentChapter = chapters.findBySlug(slug) ?: chapters.save(
+                currentChapter = chapters.findBySlug(slug)?.apply {
+                    title = p.chapterDir
+                    position = p.chapterPos
+                } ?: chapters.save(
                     ContentChapter(title = p.chapterDir, slug = slug, position = p.chapterPos),
                 )
+                currentChapter = chapters.save(currentChapter!!)
+                touchedChapters.add(currentChapter!!.id)
                 chCount += 1
                 currentSection = null
             }
             val chapter = currentChapter ?: throw BadRequestException("Не удалось определить главу")
             if (currentSection?.title != p.sectionDir) {
                 val slug = sectionSlug(p) ?: "section-${secCount + 1}"
-                currentSection = sections.findByChapterIdAndSlug(chapter.id, slug) ?: sections.save(
+                currentSection = sections.findByChapterIdAndSlug(chapter.id, slug)?.apply {
+                    title = p.sectionDir
+                    position = p.sectionPos
+                } ?: sections.save(
                     ContentSection(chapterId = chapter.id, title = p.sectionDir, slug = slug, position = p.sectionPos),
                 )
+                currentSection = sections.save(currentSection!!)
+                seenSections.add(currentSection!!.id)
                 secCount += 1
             }
             val section = currentSection ?: throw BadRequestException("Не удалось определить раздел")
@@ -489,10 +505,34 @@ class ContentService(
                 position = p.articlePos
             }
             articles.save(article)
+            seenArticles.add(article.id)
             artCount += 1
         }
 
-        return ContentImportResult(chapters = chCount, sections = secCount, articles = artCount, assets = linkRewrite.size)
+        // Синхронизация: в главах из архива удаляем разделы и статьи, которых в архиве нет.
+        for (chapterId in touchedChapters) {
+            for (section in sections.findByChapterIdOrderByPositionAscIdAsc(chapterId)) {
+                if (section.id in seenSections) {
+                    for (article in articles.findBySectionIdOrderByPositionAscIdAsc(section.id)) {
+                        if (article.id !in seenArticles) {
+                            articles.delete(article)
+                            removedCount++
+                        }
+                    }
+                } else {
+                    removedCount += articles.findBySectionIdOrderByPositionAscIdAsc(section.id).size + 1
+                    sections.delete(section)
+                }
+            }
+        }
+
+        return ContentImportResult(
+            chapters = chCount,
+            sections = secCount,
+            articles = artCount,
+            assets = linkRewrite.size,
+            removed = removedCount,
+        )
     }
 
     private fun chapterSlug(p: ParsedArticle): String? =