feat(library): add source chips to game library

Chips show only when the user has 2 or more sources.
A selected source the user lacks stays visible, so it can be cleared.

src/utils/backlog.test.js

@@ -1,5 +1,5 @@
 import {describe, expect, it} from 'vitest';
-import {backlogShare, libraryQuery, NO_PRIORITY, parseStatus, toBacklogRequest} from './backlog.js';
+import {backlogShare, libraryQuery, NO_PRIORITY, parseSources, parseStatus, toBacklogRequest} from './backlog.js';
 
 describe('toBacklogRequest', () => {
     it('sends every field', () => {
@@ -60,3 +60,18 @@ describe('libraryQuery hideDuplicates', () => {
         expect(libraryQuery({...base, hideDuplicates: false})).not.toContain('hideDuplicates');
     });
 });
+
+describe('sources', () => {
+    it('parseSources_KeepsKnownValuesInOrder', () => {
+        expect(parseSources('PSN,FOO,STEAM,PSN')).toEqual(['STEAM', 'PSN']);
+        expect(parseSources(null)).toEqual([]);
+        expect(parseSources('')).toEqual([]);
+    });
+
+    it('libraryQuery_SetsSourceOnlyWhenSelected', () => {
+        const base = {page: 0, size: 20, sort: 'appid,asc', status: null, q: ''};
+        expect(libraryQuery({...base, source: 'STEAM,PSN'})).toBe('page=0&size=20&sort=appid%2Casc&source=STEAM%2CPSN');
+        expect(libraryQuery({...base, source: ''})).not.toContain('source');
+        expect(libraryQuery(base)).not.toContain('source');
+    });
+});