feat(duplicates): add filter to show only groups where at least one song is in a playlist

packages/frontend/src/components/DuplicatesViewer.tsx

@@ -1,5 +1,5 @@
-import React, { useEffect, useState } from 'react';
-import { Box, VStack, Heading, Text, HStack, Badge, Select, Spinner, Table, Thead, Tr, Th, Tbody, Td, IconButton, Tooltip } from '@chakra-ui/react';
+import React, { useEffect, useMemo, useState } from 'react';
+import { Box, VStack, Heading, Text, HStack, Badge, Select, Spinner, Table, Thead, Tr, Th, Tbody, Td, IconButton, Tooltip, Switch } from '@chakra-ui/react';
 import { FiCheck, FiTrash2 } from 'react-icons/fi';
 import { api } from '../services/api';
 
@@ -27,6 +27,7 @@ export const DuplicatesViewer: React.FC = () => {
   const [loading, setLoading] = useState(false);
   const [minGroupSize, setMinGroupSize] = useState(2);
   const [processingGroupKey, setProcessingGroupKey] = useState<string | null>(null);
+  const [onlyWithPlaylists, setOnlyWithPlaylists] = useState(false);
 
   const loadDuplicates = async (minSize: number) => {
     setLoading(true);
@@ -45,6 +46,11 @@ export const DuplicatesViewer: React.FC = () => {
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [minGroupSize]);
 
+  const filteredGroups = useMemo(() => {
+    if (!onlyWithPlaylists) return groups;
+    return groups.filter(g => g.items.some(it => (it.playlists || []).length > 0));
+  }, [groups, onlyWithPlaylists]);
+
   return (
     <VStack spacing={4} align="stretch">
       <HStack justify="space-between">
@@ -64,16 +70,25 @@ export const DuplicatesViewer: React.FC = () => {
             <option value={3}>3+</option>
             <option value={4}>4+</option>
           </Select>
+          <HStack pl={4} spacing={2}>
+            <Text color="gray.400" fontSize="sm">Only with playlists</Text>
+            <Switch
+              size="sm"
+              isChecked={onlyWithPlaylists}
+              onChange={(e) => setOnlyWithPlaylists(e.target.checked)}
+              colorScheme="blue"
+            />
+          </HStack>
         </HStack>
       </HStack>
 
       {loading ? (
         <HStack><Spinner size="sm" /><Text color="gray.400">Scanning duplicates…</Text></HStack>
-      ) : groups.length === 0 ? (
+      ) : filteredGroups.length === 0 ? (
         <Text color="gray.500">No duplicate groups found.</Text>
       ) : (
         <VStack spacing={4} align="stretch">
-          {groups.map((group) => (
+          {filteredGroups.map((group) => (
             <Box key={group.key} p={4} bg="gray.800" borderRadius="md" borderWidth="1px" borderColor="gray.700">
               <HStack justify="space-between" mb={2}>
                 <HStack>