feat(#221): change TagInput binding to Tag[], add color dots and hierarchy grouping

Backend:
- TagRepository: add findDescendantIdsByName() recursive CTE query
- TagService: add expandTagNamesToDescendantIdSets() for document search

Frontend:
- TagInput: accept Tag[] (id, name, color, parentId) instead of string[]
- Chips show color dot via var(--c-tag-{color}) when tag has color
- Suggestions grouped hierarchically: children indented under their parents
- Update DescriptionSection, edit/new pages, SearchFilterBar, +page.svelte

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

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

@@ -34,4 +34,21 @@ public interface TagRepository extends JpaRepository<Tag, UUID> {
             SELECT parent_id FROM ancestors
             """, nativeQuery = true)
     List<UUID> findAncestorIds(@Param("tagId") UUID tagId);
+
+    /**
+     * Returns the IDs of the tag with the given name AND all of its descendants
+     * via a recursive CTE. Used to expand a selected tag to inclusive hierarchy results.
+     * Includes a depth guard of 50 levels to prevent runaway queries.
+     */
+    @Query(value = """
+            WITH RECURSIVE descendants AS (
+                SELECT id, 0 AS depth FROM tag WHERE LOWER(name) = LOWER(:name)
+                UNION ALL
+                SELECT t.id, d.depth + 1 FROM tag t
+                JOIN descendants d ON t.parent_id = d.id
+                WHERE d.depth < 50
+            )
+            SELECT id FROM descendants
+            """, nativeQuery = true)
+    List<UUID> findDescendantIdsByName(@Param("name") String name);
 }

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

@@ -2,6 +2,7 @@ package org.raddatz.familienarchiv.service;
 
 import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -16,6 +17,7 @@ import org.raddatz.familienarchiv.repository.TagRepository;
 import org.springframework.http.HttpStatus;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
+import org.springframework.util.StringUtils;
 import org.springframework.web.server.ResponseStatusException;
 
 import lombok.RequiredArgsConstructor;
@@ -71,6 +73,18 @@ public class TagService {
         tagRepository.delete(getById(id));
     }
 
+    /**
+     * For each tag name, returns the set of that tag's ID plus all descendant IDs.
+     * Used by DocumentService to expand selected filter tags before applying AND/OR logic.
+     */
+    public List<Set<UUID>> expandTagNamesToDescendantIdSets(List<String> tagNames) {
+        if (tagNames == null || tagNames.isEmpty()) return List.of();
+        return tagNames.stream()
+                .filter(StringUtils::hasText)
+                .map(name -> (Set<UUID>) new HashSet<>(tagRepository.findDescendantIdsByName(name.trim())))
+                .toList();
+    }
+
     /**
      * Returns all tags assembled into a tree. Document counts are not included here
      * (they are populated by the controller layer if needed, or set to 0).