Fix StreamsTable Group column header overflow and align with ChannelsTable

The Group column header was overflowing vertically when multiple groups were selected in the MultiSelect filter. Initial attempts to preserve sorting functionality while fixing the overflow were unsuccessful due to how Mantine's MultiSelect rightSection positioning works.

Final solution removes the sorting icon from the Group column to match ChannelsTable's implementation, where channel_group also uses a MultiSelect filter without sorting. This allows the header to properly expand vertically to accommodate selected filter values without overflow.

Resolves #613

frontend/src/components/tables/StreamsTable.jsx

@@ -856,30 +856,18 @@ const StreamsTable = ({ onReady }) => {
 
       case 'group':
         return (
-          <Flex align="center" style={{ width: '100%', flex: 1 }}>
-            <MultiSelect
-              placeholder="Group"
-              searchable
-              size="xs"
-              nothingFoundMessage="No options"
-              onClick={handleSelectClick}
-              onChange={handleGroupChange}
-              data={groupOptions}
-              variant="unstyled"
-              className="table-input-header custom-multiselect"
-              clearable
-              style={{ flex: 1, minWidth: 0 }}
-              rightSectionPointerEvents="auto"
-              rightSection={React.createElement(sortingIcon, {
-                onClick: (e) => {
-                  e.stopPropagation();
-                  onSortingChange('group');
-                },
-                size: 14,
-                style: { cursor: 'pointer' },
-              })}
-            />
-          </Flex>
+          <MultiSelect
+            placeholder="Group"
+            className="table-input-header"
+            variant="unstyled"
+            data={groupOptions}
+            size="xs"
+            searchable
+            clearable
+            onClick={handleSelectClick}
+            onChange={handleGroupChange}
+            style={{ width: '100%' }}
+          />
         );
 
       case 'm3u':