Rename API test collection references: Bookmann → Bookhoard

Bruno API test updates:
- Update test assertions: X-Bookmann-* → X-Bookhoard-*
- Update variable names and references in test scripts
- Update documentation and comments in API tests

This is part 4 of the project rename to Bookhoard.

bruno/opds/Download Book KEPUB (On-the-fly Conversion).bru

@@ -8,7 +8,7 @@
         "script": {
           "exec": [
             "// Test format-specific hash header",
-            "const kepubHash = resp.headers.get('X-Bookmann-KEPUB-SHA256');",
+            "const kepubHash = resp.headers.get('X-Bookhoard-KEPUB-SHA256');",
             "if (kepubHash) {",
             "    tests['KEPUB hash present'] = true;",
             "    tests['Hash is 64 chars'] = kepubHash.length === 64;",
@@ -16,9 +16,9 @@
             "    tests['KEPUB hash present'] = false;",
             "}",
             "",
-            "// Verify Bookmann UUID header",
-            "const bookmannUUID = resp.headers.get('X-Bookmann-UUID');",
-            "tests['Bookmann UUID present'] = bookmannUUID !== null;",
+            "// Verify Bookhoard UUID header",
+            "const bookmannUUID = resp.headers.get('X-Bookhoard-UUID');",
+            "tests['Bookhoard UUID present'] = bookmannUUID !== null;",
             "",
             "// Verify content type",
             "const contentType = resp.headers.get('Content-Type');",