Add repository field for npm provenance verification

npm rejects provenance-signed publishes (E422) when package.json has no
repository.url matching the GitHub repo recorded in the sigstore
provenance statement.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Change-Id: Ie6cf80826b6bd36ea16b430acb7098e9d1138211
diff --git a/package.json b/package.json
index 9039cd1..b335839 100644
--- a/package.json
+++ b/package.json
@@ -27,6 +27,10 @@
   },
   "author": "Marc Kupietz",
   "license": "BSD-2-Clause",
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/KorAP/conllu-cmc.git"
+  },
   "dependencies": {
     "command-line-args": "^5.2.1",
     "command-line-usage": "^7.0.1",