feat: optimize dashboard and workload queries with database indexes and SQL aggregation for improved performance

Add database indexes on ip_addresses.address and traffic_flows columns (node_id/source_ip/destination_ip/destination_port/state with updated_at) to accelerate query performance, implement ensure_runtime_indexes to create indexes on startup with IF NOT EXISTS guards, rewrite dashboard_top_talkers to use SQL aggregation with JOIN on IpAddress/TrafficFlow instead of Python loops over all

backend/app/main.py

@@ -1,5 +1,6 @@
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
+from sqlalchemy import text
 
 from app.api.v1.router import api_router
 from app.core.config import get_settings
@@ -7,6 +8,20 @@ from app.db.session import Base, SessionLocal, engine
 from app.seed.demo import seed_demo_data
 
 
+def ensure_runtime_indexes() -> None:
+    index_statements = [
+        "CREATE INDEX IF NOT EXISTS ix_ip_addresses_address ON ip_addresses (address)",
+        "CREATE INDEX IF NOT EXISTS ix_traffic_flows_node_updated ON traffic_flows (node_id, updated_at)",
+        "CREATE INDEX IF NOT EXISTS ix_traffic_flows_source_updated ON traffic_flows (source_ip, updated_at)",
+        "CREATE INDEX IF NOT EXISTS ix_traffic_flows_destination_updated ON traffic_flows (destination_ip, updated_at)",
+        "CREATE INDEX IF NOT EXISTS ix_traffic_flows_destination_port_updated ON traffic_flows (destination_port, updated_at)",
+        "CREATE INDEX IF NOT EXISTS ix_traffic_flows_state_updated ON traffic_flows (state, updated_at)",
+    ]
+    with engine.begin() as connection:
+        for statement in index_statements:
+            connection.execute(text(statement))
+
+
 def create_app() -> FastAPI:
     settings = get_settings()
     app = FastAPI(
@@ -27,6 +42,7 @@ def create_app() -> FastAPI:
     @app.on_event("startup")
     def startup() -> None:
         Base.metadata.create_all(bind=engine)
+        ensure_runtime_indexes()
         with SessionLocal() as db:
             seed_demo_data(db)
 
@@ -39,4 +55,3 @@ def create_app() -> FastAPI:
 
 
 app = create_app()
-