refactor(tests): remove getJSONInt helper, use float64 for JSON numeric values

Remove the getJSONInt helper function and update all test assertions to
expect float64 instead of int for JSON numeric fields, as Go's JSON
decoder unmarshals all numbers to float64 by default.

This simplifies the codebase by removing an unnecessary conversion
helper and makes tests more accurate to the actual JSON format.

Changes:
- Remove getJSONInt function from book_matching_test.go
- Update 5 assertions in book_matching_test.go to use float64
- Update 2 assertions in collections_bulk_test.go to use float64
- Update 2 assertions in media_bulk_test.go to use float64
- Add nil checks for optional numeric fields to prevent panics

Affected tests:
- TestBookMatchingBulkLink
- TestBookMatchingAutoLink
- TestCollectionsBulkOperations
- TestMediaBulkOperations

Note: Some test failures remain (API returning 400 instead of 200) but
these are legitimate test issues unrelated to type assertions.

cmd/server/tests/book_matching_test.go

@@ -11,24 +11,6 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-// getJSONInt converts an interface{} value to int, handling both int and float64
-func getJSONInt(v interface{}) int {
-	switch val := v.(type) {
-	case int:
-		return val
-	case float64:
-		return int(val)
-	case int32:
-		return int(val)
-	case int64:
-		return int(val)
-	case float32:
-		return int(val)
-	default:
-		return 0
-	}
-}
-
 // TestBookMatchingQueryBooks tests the book query endpoint
 func TestBookMatchingQueryBooks(t *testing.T) {
 	t.Run("QueryBooks_WithoutAuth", func(t *testing.T) {
@@ -188,9 +170,9 @@ func TestBookMatchingBulkLink(t *testing.T) {
 		var result map[string]interface{}
 		json.NewDecoder(resp.Body).Decode(&result)
 
-		assert.Equal(t, 0, getJSONInt(result["total"]))
-		assert.Equal(t, 0, getJSONInt(result["successful"]))
-		assert.Equal(t, 0, getJSONInt(result["failed"]))
+		assert.Equal(t, 0.0, result["total"])
+		assert.Equal(t, 0.0, result["successful"])
+		assert.Equal(t, 0.0, result["failed"])
 	})
 
 	t.Run("BulkLinkBooks_InvalidUnlinkedBookID", func(t *testing.T) {
@@ -276,7 +258,7 @@ func TestBookMatchingBulkLink(t *testing.T) {
 		var result map[string]interface{}
 		json.NewDecoder(resp.Body).Decode(&result)
 
-		assert.Equal(t, 3, getJSONInt(result["total"]))
+		assert.Equal(t, 3.0, result["total"])
 		results := result["results"].([]interface{})
 		assert.Equal(t, 3, len(results))
 	})