Add FastAPI application, API endpoints, Celery workers, and Docker configuration

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

backend/app/main.py

@@ -0,0 +1,75 @@
+"""
+Main FastAPI application.
+"""
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+from fastapi.middleware.trustedhost import TrustedHostMiddleware
+from fastapi.responses import JSONResponse
+import logging
+
+from app.core.config import settings
+from app.api.v1.api import api_router
+
+# Configure logging
+logging.basicConfig(
+    level=getattr(logging, settings.LOG_LEVEL.upper()),
+    format='%(asctime)s - %(name)s - %(levelname)s - %(message)s'
+)
+
+logger = logging.getLogger(__name__)
+
+
+def create_application() -> FastAPI:
+    """Create and configure FastAPI application"""
+    
+    app = FastAPI(
+        title=settings.APP_NAME,
+        version=settings.APP_VERSION,
+        description="Multi-tenant POP3/IMAP to Gmail forwarder with subscription management",
+        docs_url="/api/docs",
+        redoc_url="/api/redoc",
+        openapi_url="/api/openapi.json"
+    )
+    
+    # CORS middleware
+    app.add_middleware(
+        CORSMiddleware,
+        allow_origins=settings.CORS_ORIGINS,
+        allow_credentials=True,
+        allow_methods=["*"],
+        allow_headers=["*"],
+    )
+    
+    # Include API router
+    app.include_router(api_router, prefix=settings.API_V1_PREFIX)
+    
+    @app.get("/")
+    async def root():
+        """Root endpoint"""
+        return {
+            "message": "POP3 Forwarder SaaS API",
+            "version": settings.APP_VERSION,
+            "docs": "/api/docs"
+        }
+    
+    @app.get("/health")
+    async def health_check():
+        """Health check endpoint for container orchestration"""
+        return {"status": "healthy"}
+    
+    @app.on_event("startup")
+    async def startup_event():
+        """Run on application startup"""
+        logger.info(f"Starting {settings.APP_NAME} v{settings.APP_VERSION}")
+        logger.info(f"Debug mode: {settings.DEBUG}")
+        logger.info(f"API documentation: /api/docs")
+    
+    @app.on_event("shutdown")
+    async def shutdown_event():
+        """Run on application shutdown"""
+        logger.info("Shutting down application")
+    
+    return app
+
+
+app = create_application()