Node settings arrive as keyword arguments, not a params dict

A python node's settings are constants of its own function, so they are passed
the way its ports are: by name. The controller binds them to the compiled
function, the `params` field is gone from the worker and remote protocols, and
a setting sharing a port's name is reported as a node error rather than
shadowing it. The panel's scaffold follows suit and keeps the header in step
with both ports and settings.

The demo's `pace` moves from a flow input to a setting of the training node,
which is what it always was.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NUb8YpL2s3gmN9WTACTt4q

backend/tests/flow/test_library.py

@@ -8,7 +8,7 @@ from app.flow.messages import MessageSpec
 from app.flow.schemas import FlowDef, NodeDef
 from app.flow.store import FlowStore, LibExists, LibNotFound
 
-SOURCE = "def process(params):\n    return {'temp': 1}\n"
+SOURCE = "def process():\n    return {'temp': 1}\n"
 
 
 @pytest.fixture