Add DeepSeek/xAI/OpenAI-compatible sentiment providers; custom dark dropdown

Providers (admin-switchable, no redeploy):
- DeepSeek and any OpenAI-compatible endpoint (OpenRouter, Together,
  Groq, local Ollama) via a generic Chat Completions adapter + base_url
- xAI Grok with Live Search (search_parameters web+X, citations) —
  grounded tier alongside OpenAI and Gemini
- DeepSeek / generic compatible endpoints are ungrounded (no web
  search); UI shows an amber warning and labels each provider's grounding
- Optional env fallbacks DEEPSEEK_API_KEY / XAI_API_KEY

UI: replace native <select> (unstyleable white popup on Windows) with a
custom dark Dropdown component everywhere — sentiment provider, scanner
filters, market sort, indicators, admin universe, user role.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/unit/test_sentiment_provider_service.py

@@ -33,7 +33,8 @@ class TestGetConfig:
         assert config["model"] == "gpt-4o-mini"
         assert config["api_key_configured"] is False
         assert config["api_key_source"] == "none"
-        assert set(config["valid_providers"]) == {"openai", "gemini"}
+        assert config["web_search"] is True
+        assert set(config["valid_providers"]) == {"openai", "gemini", "deepseek", "xai", "openai_compatible"}
 
     async def test_never_returns_raw_key(self, session: AsyncSession):
         await sps.update_sentiment_config(session, api_key="sk-secret-123")
@@ -92,3 +93,38 @@ class TestBuildProvider:
         await sps.update_sentiment_config(session, provider="openai")
         provider = await sps.build_sentiment_provider(session)
         assert type(provider).__name__ == "OpenAISentimentProvider"
+
+    async def test_builds_deepseek_with_fixed_base_url(self, session: AsyncSession):
+        await sps.update_sentiment_config(session, provider="deepseek", api_key="ds-x")
+        provider = await sps.build_sentiment_provider(session)
+        assert type(provider).__name__ == "OpenAICompatibleSentimentProvider"
+        config = await sps.get_sentiment_config(session)
+        assert config["base_url"] == "https://api.deepseek.com"
+        assert config["web_search"] is False
+
+    async def test_builds_xai_with_live_search(self, session: AsyncSession):
+        await sps.update_sentiment_config(session, provider="xai", api_key="xai-x")
+        provider = await sps.build_sentiment_provider(session)
+        assert type(provider).__name__ == "OpenAICompatibleSentimentProvider"
+        # xAI is wired with Live Search enabled
+        assert provider._live_search is True
+        assert provider._extra_body == {"search_parameters": {"mode": "auto", "return_citations": True}}
+        config = await sps.get_sentiment_config(session)
+        assert config["base_url"] == "https://api.x.ai/v1"
+        assert config["web_search"] is True
+
+    async def test_openai_compatible_requires_base_url(self, session: AsyncSession):
+        await sps.update_sentiment_config(session, provider="openai_compatible", api_key="x")
+        with pytest.raises(ProviderError):
+            await sps.build_sentiment_provider(session)
+
+    async def test_openai_compatible_with_base_url(self, session: AsyncSession):
+        await sps.update_sentiment_config(
+            session,
+            provider="openai_compatible",
+            api_key="x",
+            model="llama-3.1-70b",
+            base_url="https://openrouter.ai/api/v1",
+        )
+        provider = await sps.build_sentiment_provider(session)
+        assert type(provider).__name__ == "OpenAICompatibleSentimentProvider"