fix: exclude vendor files from frontend coverage (#260)

Coverage was 31% including vendor libs. Adds .nycrc.json scoping to
first-party code.

Co-authored-by: Kpa-clawbot <259247574+Kpa-clawbot@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.nycrc.json

@@ -0,0 +1,10 @@
+{
+  "include": [
+    "public/*.js"
+  ],
+  "exclude": [
+    "public/vendor/**",
+    "public/leaflet-*.js",
+    "public/qrcode*.js"
+  ]
+}