TUL/fix: default filter operator to 'equals' for operator-less URLs (#781)

A search URL whose filter carries no operator (e.g. a legacy or crawled
"/search?f.subject=foo" instead of "f.subject=foo,equals") was forwarded to the
backend verbatim. The backend correctly rejects the operator-less filter with
HTTP 422 per the DSpace REST Contract, producing an error on every affected
search render (dataquest-dev/dspace-customers#781).

When reading active filters from the URL in SearchConfigurationService.
getCurrentFilters, default the operator to 'equals' (mirroring the existing
range-filter branch). Values that already embed an operator - i.e. contain a
comma - are left untouched by SearchOptions.toRestUrl, so explicit operators
(equals/notequals/contains/authority/...) are preserved. Operator-less legacy
URLs now resolve to "<value>,equals" and return results instead of 422.

Updated the getCurrentFilters expectations in the SearchConfigurationService
and MyDSpaceConfigurationService specs accordingly.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: milanmajchrak

src/app/core/shared/search/search-configuration.service.spec.ts

@@ -31,7 +31,7 @@ describe('SearchConfigurationService', () => {
   });
 
   const backendFilters = [
-    new SearchFilter('f.author', ['another value']),
+    new SearchFilter('f.author', ['another value'], 'equals'),
     new SearchFilter('f.date', ['[2013 TO 2018]'], 'equals')
   ];
 

src/app/core/shared/search/search-configuration.service.ts

@@ -196,7 +196,11 @@ export class SearchConfigurationService implements OnDestroy {
               filters.push(new SearchFilter(realKey, ['[' + min + ' TO ' + max + ']'], 'equals'));
             }
           } else {
-            filters.push(new SearchFilter(key, filterParams[key]));
+            // Default to the "equals" operator when a filter value carries none (e.g. a legacy or
+            // crawled URL like "f.subject=foo" instead of "f.subject=foo,equals"). Without this the
+            // backend rejects the operator-less filter with HTTP 422. Values that already embed an
+            // operator (contain a comma) keep it - see SearchOptions.toRestUrl. dspace-customers#781.
+            filters.push(new SearchFilter(key, filterParams[key], 'equals'));
           }
         });
         return filters;

src/app/my-dspace-page/my-dspace-configuration.service.spec.ts

@@ -30,7 +30,7 @@ describe('MyDSpaceConfigurationService', () => {
   });
 
   const backendFilters = [
-    new SearchFilter('f.namedresourcetype', ['another value']),
+    new SearchFilter('f.namedresourcetype', ['another value'], 'equals'),
     new SearchFilter('f.dateSubmitted', ['[2013 TO 2018]'], 'equals')
   ];