test(api): add Bruno tests for sync-kobo and OPDS features

Sync-Kobo:
- Auto link books endpoint tests
- Bulk link books endpoint tests
- Get unlinked book suggestions endpoint tests

OPDS:
- Download book with on-the-fly KEPUB conversion tests

All tests cover no user, user, and admin contexts

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

@@ -0,0 +1,35 @@
+{
+  "meta": {
+    "name": "Download Book KEPUB (On-the-fly Conversion)",
+    "type": "http",
+    "event": [
+      {
+        "listen": "test",
+        "script": {
+          "exec": [
+            "// Test format-specific hash header",
+            "const kepubHash = resp.headers.get('X-Bookmann-KEPUB-SHA256');",
+            "if (kepubHash) {",
+            "    tests['KEPUB hash present'] = true;",
+            "    tests['Hash is 64 chars'] = kepubHash.length === 64;",
+            "} else {",
+            "    tests['KEPUB hash present'] = false;",
+            "}",
+            "",
+            "// Verify Bookmann UUID header",
+            "const bookmannUUID = resp.headers.get('X-Bookmann-UUID');",
+            "tests['Bookmann UUID present'] = bookmannUUID !== null;",
+            "",
+            "// Verify content type",
+            "const contentType = resp.headers.get('Content-Type');",
+            "tests['Content-Type is KEPUB'] = contentType && contentType.includes('kepub');"
+          ]
+        }
+      }
+    ]
+  },
+  "req": {
+    "url": "{{baseUrl}}/opds/devices/{{deviceId}}/download/{{mediaItemId}}?format=kepub",
+    "method": "GET"
+  }
+}