Forecasting app: hybrid port to HNF stack

Python FastAPI ML backend kept intact; auth replaced with central hnf_session cookie verification. Frontend rebuilt on React 18 + TS + Vite with stack design system, Plotly charts retained. Shared Postgres via DATABASE_URL; schema applied on startup.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/database.py

@@ -0,0 +1,42 @@
+"""
+Database connection and session management
+"""
+import os
+from sqlalchemy.ext.asyncio import create_async_engine, AsyncSession
+from sqlalchemy.orm import sessionmaker, declarative_base
+from sqlalchemy import create_engine
+
+DATABASE_URL = os.getenv("DATABASE_URL", "postgresql://forecast:forecast_secret@localhost:5432/forecast")
+
+# Convert to async URL
+ASYNC_DATABASE_URL = DATABASE_URL.replace("postgresql://", "postgresql+asyncpg://")
+
+# Async engine for FastAPI
+async_engine = create_async_engine(ASYNC_DATABASE_URL, echo=False)
+AsyncSessionLocal = sessionmaker(
+    async_engine, class_=AsyncSession, expire_on_commit=False
+)
+
+# Sync engine for scheduler jobs and migrations
+sync_engine = create_engine(DATABASE_URL)
+SyncSessionLocal = sessionmaker(bind=sync_engine)
+
+Base = declarative_base()
+
+
+async def get_db():
+    """Dependency for FastAPI endpoints"""
+    async with AsyncSessionLocal() as session:
+        try:
+            yield session
+        finally:
+            await session.close()
+
+
+def get_sync_db():
+    """Get sync session for scheduler jobs"""
+    db = SyncSessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()