[SOURCES] Add Boxcar commuter bus GTFS feed (NJ-NYC) (#1317)

* [SOURCES] Add Boxcar commuter bus GTFS feed (NJ-NYC)

Boxcar operates private commuter bus routes between New Jersey
and New York City (13 routes, 91 trips). Feed is auto-generated
daily from live schedule data.

Feed URL: https://boxcar-gtfs.vercel.app/api/gtfs
Website: https://www.boxcar.com

* add NJ Boxcar schedule feed

* add extracted_on key

* add latest key

---------

Co-authored-by: itsjoeco <itsjoeco@users.noreply.github.com>
Co-authored-by: Ian Chan <ianchan@mobilitydata.org>

Author: itsjoeco

catalogs/sources/gtfs/schedule/us-new-jersey-boxcar-gtfs-3105.json

@@ -0,0 +1,21 @@
+{
+    "mdb_source_id": 3105,
+    "data_type": "gtfs",
+    "provider": "Boxcar",
+    "name": "Boxcar Commuter Bus",
+    "location": {
+        "country_code": "US",
+        "subdivision_name": "New Jersey",
+        "bounding_box": {
+            "minimum_latitude": 40.5700,
+            "maximum_latitude": 41.0200,
+            "minimum_longitude": -74.6500,
+            "maximum_longitude": -73.9600,
+            "extracted_on": "2026-04-10T00:00:00+00:00"
+        }
+    },
+    "urls": {
+        "direct_download": "https://boxcar-gtfs.vercel.app/api/gtfs",
+        "latest": "https://storage.googleapis.com/storage/v1/b/mdb-latest/o/us-new-jersey-boxcar-gtfs-3105.zip?alt=media"
+    }
+}