feat(agent): complete closed-loop runtime and pricing fallback

pyproject.toml

@@ -4,6 +4,7 @@ version = "0.1.0"
 description = "Social application backend"
 requires-python = ">=3.12"
 dependencies = [
+    "ag-ui-protocol>=0.1.13",
     "alembic>=1.18.3",
     "asyncpg>=0.31.0",
     "basedpyright>=1.37.2",
@@ -42,6 +43,9 @@ default = true
 testpaths = ["backend/tests"]
 addopts = "-q"
 asyncio_mode = "auto"
+markers = [
+    "live: requires running local runtime and real external dependencies",
+]
 
 [dependency-groups]
 dev = [