Fold the brain and health screens into Home

Home is the one overview now: the brain graph flat across the top, the flow
switches, then the health sections. The /brain and /health routes and their
sidebar entries are gone.

- charts report their cursor and clicks, so hovering one filters the list
  beside it to that minute and a click pins it until Escape or Clear
- chart values round to about three significant digits, the legend mounts
  under the plot so it can wrap without leaving the card, and axis ticks
  shorten past a thousand
- the embedded brain leaves the wheel to the page rather than zooming
- number fields no longer draw their up/down spinner (NOTEPAD)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017MeiWk3Yq12n2pTvnQWYvt

ROADMAP.md

@@ -175,16 +175,20 @@ React + Vite, primarily desktop but usable on mobile. See `docs/architecture/str
       channels/rules each get a sidebar page, and the OAuth clients an agent
       registers are listed and revocable under Admin — which needed its
       management endpoints written first
-- [x] Health screen: how the engine is doing now (nodes, flows, queue, loop lag)
+- [x] Health sections: how the engine is doing now (nodes, flows, queue, loop lag)
       over what it has been doing all day — throughput and failure charts, a
       per-flow table, the recent cascades, failures that expand to their
-      traceback, dead-lettered work and the audit trail
-- [x] Brain graph: every published flow on one canvas, with nodes that talk to the
+      traceback, dead-lettered work and the audit trail. Hovering a chart
+      filters the list beside it to that minute and a click pins it
+- [x] Brain graph: every published flow at once, with nodes that talk to the
       same outside thing — a broker topic, a URL, a bucket — drawn as a single
       neuron, so the wiring that runs between flows through a broker is visible at
       all. Laid out by a force simulation settled once and then frozen, lit by the
       same socket the editor listens to, and read-only: a neuron leads back to the
       flow it came from
+- [x] Both of the above sit on Home rather than at routes of their own: the brain
+      flat across the top, the health sections under the flow switches. One
+      overview instead of three
 - [x] Mobile-friendly canvas: touch connect, full-screen node panel
 - [ ] Installable as a PWA (`vite-plugin-pwa`)