Align backend authentication and API response contracts

Replace cookie authentication with revocable Bearer sessions, optional one-use PNG challenges, bounded login limits, and short-lived market WebSocket tickets. Keep captcha disabled by default.

Standardize ordinary JSON responses while preserving HTTP statuses, raw OpenAPI, redirects, SSE, and WebSocket semantics. Revoke long connections with their owning session.

Expose official calendar data and collector status to the frontend and research tools, support bilingual news topics, and keep summaries and forward-only labels explicit. Verify the staged snapshot with all 305 backend tests.

backend/tests/test_research_accounting.py

@@ -19,7 +19,7 @@ def test_forward_endpoint_excludes_labels_at_or_after_entry(trading):
     class Session:
         async def execute(self, statement):
             return SimpleNamespace(all=lambda: rows)
-    result = asyncio.run(list_news_signals(Session()))
+    result = asyncio.run(list_news_signals(Session())).data
     assert result.labeled == result.filled == 1
     assert [item.news_id for item in result.recent] == [1]
     assert all(s.n == 1 for s in result.stats)