feat(amazon): add marketplace locale mapping

surfsense_backend/app/proprietary/platforms/amazon/locale.py

@@ -0,0 +1,33 @@
+"""Marketplace locale helpers for Amazon fetch routing.
+
+Only proxy countries verified against the configured DataImpulse plan are mapped
+here. Unmapped marketplaces fall back to the default proxy exit.
+"""
+
+_MARKETPLACE_COUNTRY = {
+    "com": "us",
+    "co.uk": "gb",
+    "de": "de",
+    "fr": "fr",
+    "it": "it",
+    "es": "es",
+}
+
+_MARKETPLACE_LANGUAGE = {
+    "com": "en-US",
+    "co.uk": "en-GB",
+    "de": "de-DE",
+    "fr": "fr-FR",
+    "it": "it-IT",
+    "es": "es-ES",
+}
+
+
+def proxy_country_for(marketplace: str | None) -> str | None:
+    """Return a confirmed proxy exit country for one Amazon marketplace."""
+    return _MARKETPLACE_COUNTRY.get((marketplace or "").lower())
+
+
+def accept_language_for(marketplace: str | None) -> str:
+    """Return the browser language header that matches the marketplace UI."""
+    return _MARKETPLACE_LANGUAGE.get((marketplace or "").lower(), "en-US")