test: фаза 4 — тесты extractors, ecosystem, i18n, metrics

- test_nexus.py: extract_pypi/go/npm, dispatch, edge cases (16 тестов)
- test_i18n.py: RU/EN переводы, fallback, форматирование, web UI (10 тестов)
- test_metrics.py: Prometheus endpoint (4 теста)
- test_webhooks.py: _detect_ecosystem (6 тестов), Go/npm webhook fixtures
- conftest.py: sample_nexus_go/npm_webhook fixtures
- Всего: 85 тестов (было 50)

tests/test_i18n.py

@@ -0,0 +1,47 @@
+"""Tests for i18n module."""
+
+import pytest
+
+from guarddog_nexus.i18n import LANGUAGES, t
+
+
+class TestTranslate:
+    def test_english(self):
+        assert t("nav_dashboard", "en") == "Dashboard"
+        assert t("nav_scans", "en") == "Scans"
+
+    def test_russian(self):
+        assert t("nav_dashboard", "ru") == "Панель"
+        assert t("nav_scans", "ru") == "Сканирования"
+
+    def test_default_lang(self):
+        assert t("nav_dashboard") == "Dashboard"
+
+    def test_unknown_key(self):
+        assert t("nonexistent_key", "en") == "nonexistent_key"
+
+    def test_unknown_lang_falls_back(self):
+        assert t("nav_dashboard", "fr") == "Dashboard"
+
+    def test_positional_formatting(self):
+        result = t("total_scans", "en", 42)
+        assert "42" in result
+        assert "total scans" in result.lower()
+
+    def test_languages_dict(self):
+        assert "en" in LANGUAGES
+        assert "ru" in LANGUAGES
+
+
+@pytest.mark.asyncio
+async def test_web_lang_ru(client):
+    resp = await client.get("/scans?lang=ru")
+    assert resp.status_code == 200
+    assert "Сканирования" in resp.text
+
+
+@pytest.mark.asyncio
+async def test_web_lang_en(client):
+    resp = await client.get("/scans?lang=en")
+    assert resp.status_code == 200
+    assert "Scans" in resp.text