feat(metadata): add CivArchive API toggle and provider fallback order settings

- Add enable_civarchive_api toggle (default on) to allow disabling
  CivArchive to avoid its rate-limit windows entirely
- Add metadata_provider_order dropdown with two presets:
  CivitAI → CivArchive → Archive DB (default) and
  CivitAI → Archive DB → CivArchive
- Wire both settings through backend (metadata_service, settings_manager,
  misc_handlers) and frontend (SettingsManager, state, settings modal)
- Reorder Metadata section in settings modal: toggles → status/management
  → fallback order, for natural top-down workflow
- Make update_metadata_providers() log the effective provider chain
  using actually-registered providers rather than settings assumptions
- Add 5 test cases covering all provider-combination paths
- Complete i18n translations for 6 new keys across all 9 non-English locales

tests/services/test_metadata_service.py

@@ -60,3 +60,114 @@ async def test_get_metadata_provider_returns_fallback_as_is(monkeypatch):
     provider = await metadata_service.get_metadata_provider()
 
     assert provider is fallback
+
+
+# ---------------------------------------------------------------------------
+# initialize_metadata_providers — provider gating + fallback ordering
+# ---------------------------------------------------------------------------
+
+
+def _stub_settings(**overrides):
+    """Minimal settings stub returning configured values."""
+    base = {
+        "enable_metadata_archive_db": False,
+        "enable_civarchive_api": True,
+        "metadata_provider_order": "civitai_archive_sqlite",
+    }
+    base.update(overrides)
+    return SimpleNamespace(get=lambda key, default=None: base.get(key, default))
+
+
+async def _run_initialize(monkeypatch, settings):
+    # Fresh provider manager for each test
+    monkeypatch.setattr(
+        metadata_service.ModelMetadataProviderManager,
+        "get_instance",
+        AsyncMock(return_value=metadata_service.ModelMetadataProviderManager()),
+    )
+    monkeypatch.setattr(
+        metadata_service, "get_settings_manager", lambda: settings
+    )
+    monkeypatch.setattr(
+        metadata_service.ServiceRegistry,
+        "get_civitai_client",
+        AsyncMock(return_value=object()),
+    )
+    monkeypatch.setattr(
+        metadata_service.ServiceRegistry,
+        "get_civarchive_client",
+        AsyncMock(return_value=object()),
+    )
+
+    # Make MetadataArchiveManager report a usable db path when enabled
+    fake_archive = SimpleNamespace(get_database_path=lambda: "/tmp/fake.db")
+    monkeypatch.setattr(
+        metadata_service, "MetadataArchiveManager", lambda _base: fake_archive
+    )
+    # Pretend the db file exists
+    monkeypatch.setattr(metadata_service.os.path, "exists", lambda _p: True)
+
+    manager = await metadata_service.initialize_metadata_providers()
+    return manager
+
+
+def _fallback_provider_order(manager):
+    """Return the ordered list of provider labels inside the fallback provider."""
+    fallback = manager.providers.get("fallback")
+    assert isinstance(fallback, FallbackMetadataProvider), "expected a fallback provider"
+    return list(fallback._provider_labels)
+
+
+@pytest.mark.asyncio
+async def test_initialize_providers_default_order(monkeypatch):
+    settings = _stub_settings(enable_metadata_archive_db=True)
+    manager = await _run_initialize(monkeypatch, settings)
+    assert _fallback_provider_order(manager) == ["civitai_api", "civarchive_api", "sqlite"]
+
+
+@pytest.mark.asyncio
+async def test_initialize_providers_prefer_sqlite_order(monkeypatch):
+    settings = _stub_settings(
+        enable_metadata_archive_db=True,
+        metadata_provider_order="civitai_sqlite_archive",
+    )
+    manager = await _run_initialize(monkeypatch, settings)
+    assert _fallback_provider_order(manager) == ["civitai_api", "sqlite", "civarchive_api"]
+
+
+@pytest.mark.asyncio
+async def test_initialize_providers_disables_civarchive(monkeypatch):
+    settings = _stub_settings(
+        enable_metadata_archive_db=True,
+        enable_civarchive_api=False,
+    )
+    manager = await _run_initialize(monkeypatch, settings)
+    # civarchive_api must not be registered at all
+    assert "civarchive_api" not in manager.providers
+    assert _fallback_provider_order(manager) == ["civitai_api", "sqlite"]
+
+
+@pytest.mark.asyncio
+async def test_initialize_providers_skips_unavailable_sqlite_in_preset(monkeypatch):
+    # Preset wants sqlite before civarchive, but archive db is disabled ->
+    # sqlite is unavailable and must be skipped, civarchive stays.
+    settings = _stub_settings(
+        enable_metadata_archive_db=False,
+        metadata_provider_order="civitai_sqlite_archive",
+    )
+    manager = await _run_initialize(monkeypatch, settings)
+    assert _fallback_provider_order(manager) == ["civitai_api", "civarchive_api"]
+
+
+@pytest.mark.asyncio
+async def test_initialize_providers_single_provider_when_only_civitai(monkeypatch):
+    # Both archive db and civarchive disabled -> only civitai_api remains,
+    # which takes the single-provider path (registered as default, no fallback).
+    settings = _stub_settings(
+        enable_metadata_archive_db=False,
+        enable_civarchive_api=False,
+    )
+    manager = await _run_initialize(monkeypatch, settings)
+    assert "fallback" not in manager.providers
+    assert manager.default_provider == "civitai_api"
+