feat(#221): add AND/OR tag filtering with hierarchy expansion in document search

- Replace hasTags(List<String>) spec with hasTags(List<Set<UUID>>, useOr)
- AND mode: one EXISTS subquery per expanded tag ID set; empty set = disjunction
- OR mode: union of all expanded sets into a single EXISTS subquery
- DocumentService calls tagService.expandTagNamesToDescendantIdSets() before building spec
- DocumentController exposes ?tagOp=AND|OR query param (default AND)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/main/java/org/raddatz/familienarchiv/controller/DocumentController.java

@@ -204,11 +204,12 @@ public class DocumentController {
             @RequestParam(required = false) String tagQ,
             @Parameter(description = "Filter by document status") @RequestParam(required = false) DocumentStatus status,
             @Parameter(description = "Sort field") @RequestParam(required = false) DocumentSort sort,
-            @Parameter(description = "Sort direction: ASC or DESC") @RequestParam(required = false, defaultValue = "DESC") String dir) {
+            @Parameter(description = "Sort direction: ASC or DESC") @RequestParam(required = false, defaultValue = "DESC") String dir,
+            @Parameter(description = "Tag operator: AND (default) or OR") @RequestParam(required = false) String tagOp) {
         if (!"ASC".equalsIgnoreCase(dir) && !"DESC".equalsIgnoreCase(dir)) {
             throw new ResponseStatusException(HttpStatus.BAD_REQUEST, "dir must be ASC or DESC");
         }
-        return ResponseEntity.ok(documentService.searchDocuments(q, from, to, senderId, receiverId, tags, tagQ, status, sort, dir));
+        return ResponseEntity.ok(documentService.searchDocuments(q, from, to, senderId, receiverId, tags, tagQ, status, sort, dir, tagOp));
     }
 
     // --- TRAINING LABELS ---

backend/src/main/java/org/raddatz/familienarchiv/repository/DocumentSpecifications.java

@@ -4,6 +4,7 @@ import jakarta.persistence.criteria.*;
 import java.time.LocalDate;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Set;
 import java.util.UUID;
 
 import org.raddatz.familienarchiv.model.Document;
@@ -54,34 +55,64 @@ public class DocumentSpecifications {
         return (root, query, cb) -> status == null ? null : cb.equal(root.get("status"), status);
     }
 
-    // Filtert nach Schlagworten (UND-Verknüpfung, exakter Match)
-    public static Specification<Document> hasTags(List<String> tags) {
+    /**
+     * Filtert nach vorausgeweiteten Tag-ID-Sets mit AND- oder OR-Logik.
+     *
+     * <p>AND (useOr=false): Das Dokument muss mindestens einen Tag aus <em>jedem</em> Set besitzen.
+     * <p>OR (useOr=true): Das Dokument muss mindestens einen Tag aus der Vereinigung aller Sets besitzen.
+     *
+     * <p>Jedes Set repräsentiert einen ausgewählten Tag inklusive aller seiner Nachkommen
+     * (vorausgeweitet durch {@code TagRepository.findDescendantIdsByName}).
+     */
+    public static Specification<Document> hasTags(List<Set<UUID>> tagIdSets, boolean useOr) {
         return (root, query, cb) -> {
-            if (tags == null || tags.isEmpty())
+            if (tagIdSets == null || tagIdSets.isEmpty())
                 return null;
 
-            List<Predicate> predicates = new ArrayList<>();
-
-            for (String tagName : tags) {
-                if (!StringUtils.hasText(tagName)) continue;
-
-                Subquery<Long> subquery = query.subquery(Long.class);
-                Root<Document> subRoot = subquery.from(Document.class);
-                Join<Document, Tag> subTags = subRoot.join("tags");
-
-                subquery.select(subRoot.get("id"))
-                        .where(
-                                cb.equal(subRoot.get("id"), root.get("id")),
-                                cb.equal(cb.lower(subTags.get("name")), tagName.trim().toLowerCase())
-                        );
-
-                predicates.add(cb.exists(subquery));
+            if (!useOr) {
+                // AND mode: an empty set means the tag resolved to no IDs (doesn't exist) —
+                // no document can satisfy the condition, so return no results immediately.
+                boolean hasEmptySet = tagIdSets.stream().anyMatch(s -> s == null || s.isEmpty());
+                if (hasEmptySet) return cb.disjunction();
             }
 
+            List<Set<UUID>> nonEmpty = tagIdSets.stream()
+                    .filter(s -> s != null && !s.isEmpty())
+                    .toList();
+            if (nonEmpty.isEmpty()) return null;
+
+            if (useOr) {
+                Set<UUID> union = new java.util.HashSet<>();
+                nonEmpty.forEach(union::addAll);
+                return documentHasTagIn(root, query, cb, union);
+            }
+
+            // AND: one EXISTS subquery per set
+            List<Predicate> predicates = new ArrayList<>();
+            for (Set<UUID> ids : nonEmpty) {
+                predicates.add(documentHasTagIn(root, query, cb, ids));
+            }
             return cb.and(predicates.toArray(new Predicate[0]));
         };
     }
 
+    private static Predicate documentHasTagIn(
+            Root<Document> root,
+            jakarta.persistence.criteria.CriteriaQuery<?> query,
+            jakarta.persistence.criteria.CriteriaBuilder cb,
+            Set<UUID> tagIds) {
+        Subquery<UUID> subquery = query.subquery(UUID.class);
+        Root<Document> subRoot = subquery.from(Document.class);
+        Join<Document, Tag> subTags = subRoot.join("tags");
+
+        subquery.select(subRoot.get("id"))
+                .where(
+                        cb.equal(subRoot.get("id"), root.get("id")),
+                        subTags.get("id").in(tagIds)
+                );
+        return cb.exists(subquery);
+    }
+
     // Filtert nach partiellem Tag-Namen (ILIKE) — für Live-Tag-Suche
     public static Specification<Document> hasTagPartial(String tagQ) {
         return (root, query, cb) -> {

backend/src/main/java/org/raddatz/familienarchiv/service/DocumentService.java

@@ -293,7 +293,7 @@ public class DocumentService {
     }
 
     // 1. Allgemeine Suche (für das Suchfeld im Frontend)
-    public DocumentSearchResult searchDocuments(String text, LocalDate from, LocalDate to, UUID sender, UUID receiver, List<String> tags, String tagQ, DocumentStatus status, DocumentSort sort, String dir) {
+    public DocumentSearchResult searchDocuments(String text, LocalDate from, LocalDate to, UUID sender, UUID receiver, List<String> tags, String tagQ, DocumentStatus status, DocumentSort sort, String dir, String tagOperator) {
         boolean hasText = StringUtils.hasText(text);
         List<UUID> rankedIds = null;
 
@@ -302,12 +302,15 @@ public class DocumentService {
             if (rankedIds.isEmpty()) return DocumentSearchResult.withMatchData(List.of(), Map.of());
         }
 
+        boolean useOrLogic = "OR".equalsIgnoreCase(tagOperator);
+        List<Set<UUID>> expandedTagSets = tagService.expandTagNamesToDescendantIdSets(tags);
+
         Specification<Document> textSpec = hasText ? hasIds(rankedIds) : (root, query, cb) -> null;
         Specification<Document> spec = Specification.where(textSpec)
                 .and(isBetween(from, to))
                 .and(hasSender(sender))
                 .and(hasReceiver(receiver))
-                .and(hasTags(tags))
+                .and(hasTags(expandedTagSets, useOrLogic))
                 .and(hasTagPartial(tagQ))
                 .and(hasStatus(status));