Add flow settings, pulse emitting nodes, and simplify node state

- One dot per node now carries the whole story: primary while running, sage
  after a good run, red when anything is wrong, with the explanation on hover.
  The corner badge is gone, along with the second way of saying the same thing.
- A node that publishes something flashes a ring, so a running flow is legible
  without reading the edge values. Nodes that consume but publish nothing stay
  quiet, which is why the event carries an output count.
- Flow settings open in the same panel its nodes use, from a pencil in the
  dock: the title, the name, and deleting the flow. NodePanel and FlowPanel
  share the panel chrome rather than each drawing their own.
- Renaming is a server operation, because a flow's name is the namespace of its
  messages: the directory moves and every other flow reading `old.message` is
  repointed, instead of being left pointing at a flow that no longer exists.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016WzrvW7rjQbynnhF6pxh6i

backend/tests/flow/test_store.py

@@ -5,7 +5,7 @@ import pytest
 
 from app.flow.messages import MessageSpec
 from app.flow.schemas import FlowDef, NodeDef
-from app.flow.store import FlowNotFound, FlowStore
+from app.flow.store import FlowExists, FlowNotFound, FlowStore
 
 
 @pytest.fixture
@@ -73,3 +73,47 @@ def test_deleting_removes_flow_and_its_nodes(store: FlowStore):
 
     assert store.list_flows() == []
     assert not (store.root / "heating").exists()
+
+
+def test_renaming_a_flow_carries_its_nodes(store: FlowStore):
+    store.write_flow(a_flow())
+    store.write_node_source(
+        "heating", "sensor", "def process(params):\n    return {}\n"
+    )
+
+    renamed = store.rename_flow("heating", "warmth")
+
+    assert renamed.name == "warmth"
+    assert store.list_flows() == ["warmth"]
+    assert "def process" in store.read_node_source("warmth", "sensor")
+
+
+def test_renaming_a_flow_repoints_the_flows_reading_it(store: FlowStore):
+    store.write_flow(a_flow())
+    store.write_flow(
+        FlowDef(
+            name="display",
+            nodes=[
+                NodeDef(
+                    id="gauge",
+                    # Reads across the flow boundary, so the name must follow.
+                    requires=[MessageSpec(name="heating.temp")],
+                )
+            ],
+        )
+    )
+
+    store.rename_flow("heating", "warmth")
+
+    display = store.read_flow("display")
+    assert display.nodes[0].requires[0].name == "warmth.temp"
+
+
+def test_renaming_onto_an_existing_name_is_refused(store: FlowStore):
+    store.write_flow(a_flow())
+    store.write_flow(FlowDef(name="warmth"))
+
+    with pytest.raises(FlowExists):
+        store.rename_flow("heating", "warmth")
+
+    assert store.list_flows() == ["heating", "warmth"]