feat: auto-detect timezone/locale from proxy IP via geoip

Adds geoip=True parameter to launch(), launch_async(), and
launch_context(). Resolves proxy exit IP → MaxMind GeoLite2-City
lookup → timezone + locale. Downloads ~70MB DB on first use from
P3TERX mirror, caches in ~/.cloakbrowser/geoip/.

Optional deps: pip install cloakbrowser[geoip] / npm install mmdb-lib
Explicit timezone/locale always override auto-detected values.

tests/test_geoip.py

@@ -0,0 +1,138 @@
+"""Unit tests for GeoIP-based timezone/locale detection."""
+
+from unittest.mock import patch
+
+import pytest
+
+from cloakbrowser.browser import _maybe_resolve_geoip
+from cloakbrowser.geoip import (
+    COUNTRY_LOCALE_MAP,
+    _resolve_proxy_ip,
+)
+
+
+# ---------------------------------------------------------------------------
+# _resolve_proxy_ip
+# ---------------------------------------------------------------------------
+
+
+def test_resolve_literal_ipv4():
+    assert _resolve_proxy_ip("http://10.50.96.5:8888") == "10.50.96.5"
+
+
+def test_resolve_literal_ipv4_with_auth():
+    assert _resolve_proxy_ip("http://user:pass@10.50.96.5:8888") == "10.50.96.5"
+
+
+def test_resolve_literal_ipv6():
+    ip = _resolve_proxy_ip("http://[::1]:8888")
+    assert ip == "::1"
+
+
+def test_resolve_hostname():
+    """DNS resolution of a known hostname should return an IP."""
+    ip = _resolve_proxy_ip("http://localhost:8888")
+    assert ip is not None
+    assert ip in ("127.0.0.1", "::1")
+
+
+def test_resolve_invalid_url():
+    assert _resolve_proxy_ip("not-a-url") is None
+
+
+def test_resolve_empty():
+    assert _resolve_proxy_ip("") is None
+
+
+# ---------------------------------------------------------------------------
+# COUNTRY_LOCALE_MAP
+# ---------------------------------------------------------------------------
+
+
+def test_locale_map_has_common_countries():
+    for code in ("US", "GB", "DE", "FR", "JP", "BR", "IL", "RU"):
+        assert code in COUNTRY_LOCALE_MAP, f"Missing {code}"
+
+
+def test_locale_map_values_are_bcp47():
+    """All locales should be language-REGION format."""
+    for code, locale in COUNTRY_LOCALE_MAP.items():
+        parts = locale.split("-")
+        assert len(parts) == 2, f"{code}: {locale} not language-REGION"
+        assert parts[0].islower(), f"{code}: language part should be lowercase"
+        assert parts[1].isupper(), f"{code}: region part should be uppercase"
+
+
+# ---------------------------------------------------------------------------
+# resolve_proxy_geo fallbacks
+# ---------------------------------------------------------------------------
+
+
+def test_resolve_geo_raises_when_geoip2_missing():
+    """Should raise ImportError with install instructions when geoip2 not installed."""
+    with patch.dict("sys.modules", {"geoip2": None, "geoip2.database": None}):
+        from importlib import reload
+        import cloakbrowser.geoip as geoip_mod
+        reload(geoip_mod)
+        with pytest.raises(ImportError, match="pip install cloakbrowser"):
+            geoip_mod.resolve_proxy_geo("http://10.50.96.5:8888")
+        # Restore
+        reload(geoip_mod)
+
+
+def test_resolve_geo_returns_none_when_db_missing():
+    """Should return (None, None) when DB file doesn't exist."""
+    mock_geoip2 = type("module", (), {"database": type("db", (), {"Reader": None})})()
+    with patch.dict("sys.modules", {"geoip2": mock_geoip2, "geoip2.database": mock_geoip2.database}):
+        with patch("cloakbrowser.geoip._ensure_geoip_db", return_value=None):
+            with patch("cloakbrowser.geoip._resolve_exit_ip", return_value=None):
+                from cloakbrowser.geoip import resolve_proxy_geo
+                assert resolve_proxy_geo("http://10.50.96.5:8888") == (None, None)
+
+
+# ---------------------------------------------------------------------------
+# _maybe_resolve_geoip (browser.py helper)
+# ---------------------------------------------------------------------------
+
+
+def test_maybe_resolve_skips_when_geoip_false():
+    tz, loc = _maybe_resolve_geoip(False, "http://proxy:8080", None, None)
+    assert tz is None
+    assert loc is None
+
+
+def test_maybe_resolve_skips_when_no_proxy():
+    tz, loc = _maybe_resolve_geoip(True, None, None, None)
+    assert tz is None
+    assert loc is None
+
+
+def test_maybe_resolve_skips_when_both_explicit():
+    """Explicit values should not trigger geoip resolution."""
+    tz, loc = _maybe_resolve_geoip(True, "http://proxy:8080", "Europe/Berlin", "de-DE")
+    assert tz == "Europe/Berlin"
+    assert loc == "de-DE"
+
+
+def test_maybe_resolve_fills_missing_timezone():
+    """When only locale is explicit, geoip should fill timezone."""
+    with patch("cloakbrowser.geoip.resolve_proxy_geo", return_value=("America/New_York", "en-US")):
+        tz, loc = _maybe_resolve_geoip(True, "http://proxy:8080", None, "fr-FR")
+        assert tz == "America/New_York"
+        assert loc == "fr-FR"  # Explicit wins
+
+
+def test_maybe_resolve_fills_missing_locale():
+    """When only timezone is explicit, geoip should fill locale."""
+    with patch("cloakbrowser.geoip.resolve_proxy_geo", return_value=("America/New_York", "en-US")):
+        tz, loc = _maybe_resolve_geoip(True, "http://proxy:8080", "Asia/Tokyo", None)
+        assert tz == "Asia/Tokyo"  # Explicit wins
+        assert loc == "en-US"
+
+
+def test_maybe_resolve_fills_both():
+    """When neither is set, geoip should fill both."""
+    with patch("cloakbrowser.geoip.resolve_proxy_geo", return_value=("Europe/Berlin", "de-DE")):
+        tz, loc = _maybe_resolve_geoip(True, "http://proxy:8080", None, None)
+        assert tz == "Europe/Berlin"
+        assert loc == "de-DE"