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/index.css

@@ -35,8 +35,8 @@
   --ease-emphasized: cubic-bezier(0.2, 0, 0, 1);
   --ease-standard: cubic-bezier(0.4, 0, 0.2, 1);
   --duration-fast: 150ms;
-  --duration-base: 200ms;
-  --duration-slow: 300ms;
+  --duration-base: 250ms;
+  --duration-slow: 500ms;
   --color-background: var(--background);
   --color-foreground: var(--foreground);
   --color-card: var(--card);