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

frontend/src/components/Flow/flow.css

@@ -49,6 +49,30 @@
   }
 }
 
+/* A node that just published something says so, once, and settles. */
+@media (prefers-reduced-motion: no-preference) {
+  .node-pulse {
+    position: absolute;
+    inset: -3px;
+    border-radius: inherit;
+    border: 2px solid var(--primary);
+    box-shadow: 0 0 0 3px color-mix(in srgb, var(--primary) 18%, transparent);
+    pointer-events: none;
+    animation: node-pulse var(--duration-slow) var(--ease-emphasized) forwards;
+  }
+
+  @keyframes node-pulse {
+    from {
+      opacity: 1;
+      transform: scale(1);
+    }
+    to {
+      opacity: 0;
+      transform: scale(1.09);
+    }
+  }
+}
+
 /* Handles are neutral: the one brand-secondary affordance here is Run. */
 .react-flow__handle {
   width: 12px;