feat: Transform to web architecture with FastAPI backend

This major update transforms leggen from CLI-only to a web-ready
architecture while maintaining full CLI compatibility.

New Features:
- FastAPI backend service (leggend) with comprehensive REST API
- Background job scheduler with configurable cron (replaces Ofelia)
- All CLI commands refactored to use API endpoints
- Docker configuration updated for new services
- API client with health checks and error handling

API Endpoints:
- /api/v1/banks/* - Bank connections and institutions
- /api/v1/accounts/* - Account management and balances
- /api/v1/transactions/* - Transaction retrieval with filtering
- /api/v1/sync/* - Manual sync and scheduler configuration
- /api/v1/notifications/* - Notification settings management

CLI Enhancements:
- New --api-url option and LEGGEND_API_URL environment variable
- Enhanced sync command with --wait and --force options
- Improved transactions command with --full and --limit options
- Automatic fallback and health checking

Breaking Changes:
- compose.yml structure updated (leggend service added)
- Ofelia scheduler removed (internal scheduler used instead)

🤖 Generated with [Claude Code](https://claude.ai/code)

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

leggend/main.py

@@ -0,0 +1,84 @@
+import asyncio
+from contextlib import asynccontextmanager
+
+import uvicorn
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+from loguru import logger
+
+from leggend.api.routes import banks, accounts, sync, notifications
+from leggend.background.scheduler import scheduler
+from leggend.config import config
+
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    # Startup
+    logger.info("Starting leggend service...")
+    
+    # Load configuration
+    try:
+        config.load_config()
+        logger.info("Configuration loaded successfully")
+    except Exception as e:
+        logger.error(f"Failed to load configuration: {e}")
+        raise
+
+    # Start background scheduler
+    scheduler.start()
+    logger.info("Background scheduler started")
+    
+    yield
+    
+    # Shutdown
+    logger.info("Shutting down leggend service...")
+    scheduler.shutdown()
+
+
+def create_app() -> FastAPI:
+    app = FastAPI(
+        title="Leggend API",
+        description="Open Banking API for Leggen",
+        version="0.6.11",
+        lifespan=lifespan,
+    )
+
+    # Add CORS middleware
+    app.add_middleware(
+        CORSMiddleware,
+        allow_origins=["http://localhost:3000", "http://localhost:5173"],  # SvelteKit dev servers
+        allow_credentials=True,
+        allow_methods=["*"],
+        allow_headers=["*"],
+    )
+
+    # Include API routes
+    app.include_router(banks.router, prefix="/api/v1", tags=["banks"])
+    app.include_router(accounts.router, prefix="/api/v1", tags=["accounts"])
+    app.include_router(sync.router, prefix="/api/v1", tags=["sync"])
+    app.include_router(notifications.router, prefix="/api/v1", tags=["notifications"])
+
+    @app.get("/")
+    async def root():
+        return {"message": "Leggend API is running", "version": "0.6.11"}
+
+    @app.get("/health")
+    async def health():
+        return {"status": "healthy", "config_loaded": config._config is not None}
+
+    return app
+
+
+def main():
+    app = create_app()
+    uvicorn.run(
+        app,
+        host="0.0.0.0",
+        port=8000,
+        log_level="info",
+        access_log=True,
+    )
+
+
+if __name__ == "__main__":
+    main()