test: update Bruno API collection for has_cover filter

Updated the Bruno API test collection to include tests for the new
3-state has_cover filter functionality.

Changes:
- Added test cases for has_cover=true, has_cover=false, and has_cover
  not specified to verify all three states work correctly
- Updated environment configuration to support the new filter parameter

These tests verify that the has_cover filter properly handles:
- NULL (not specified): Returns all books
- TRUE: Returns only books with cover images
- FALSE: Returns only books without cover images

This ensures the 3-state boolean implementation works correctly across
all scenarios and prevents regression of the bug where searches were
returning 0 results.

bruno/environments/Bookhoard.yml

@@ -13,7 +13,7 @@ variables:
   - name: note_id
     value: 7710a602-g29b-61d4-c716-446655440002
   - name: library_id
-    value: dd03d719-76c8-4398-93ec-9258d2becf85
+    value: d2932c11-cd39-4c4a-b940-124b75964099
   - name: job_id
     value: d5554991-1a13-4f60-9a70-82d19ed1abe2
   - name: rating