feat(postcodes/MF): add Saint-Martin (French part) postcode (#1039) (#1416)

Adds the single Saint-Martin (French side) postal code 97150.
Country-only — no state-level subdivisions in this dataset.

97150 is the canonical French postal code for the entire French part
of Saint Martin, including Marigot (capital), Grand-Case, and other
districts.

Refs: #1039

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: dr5hn

contributions/postcodes/MF.json

@@ -0,0 +1,10 @@
+[
+  {
+    "code": "97150",
+    "country_id": 190,
+    "country_code": "MF",
+    "locality_name": "Saint-Martin",
+    "type": "full",
+    "source": "manual"
+  }
+]