Add the flow editor: canvas, node panel and live values

The browser half of M3. Flows open on a full-bleed canvas with their chrome
floating over it: flow tabs top, dock bottom, node settings in a panel on the
right that leaves the graph visible and running behind it.

- Connections are derived, not stored. A node declares the messages it reads
  and publishes; every matching pair draws an edge, so two producers of one
  message converge on their consumer. Dragging output to input is shorthand
  for pointing that input at the producer's message, and asks before it
  replaces an existing one.
- Values land on the edges as they flow, over a websocket that feeds a store
  outside React, so a value arriving re-renders its own chip and nothing else.
  Clicking an edge shows the last payload and when it arrived.
- Node source is edited in Monaco, loaded only when a panel opens and themed
  from the design tokens.
- Edits autosave; identical documents are skipped server-side, so a quiet
  canvas writes nothing.
- Validation from the API shows on the node it belongs to and is summarised in
  the dock, where each entry pans to its node.
- Works on a phone: touch-connect, 44px dock targets, and the node panel
  becomes a full-screen sheet.

Two new tokens (--status-success, --font-mono) are mirrored in the website repo
and recorded in DESIGN-GUIDELINES.md.

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

frontend/src/routes/_canvas.tsx

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+import { createFileRoute, Outlet, redirect } from "@tanstack/react-router"
+
+import AppSidebar from "@/components/Sidebar/AppSidebar"
+import { SidebarInset, SidebarProvider } from "@/components/ui/sidebar"
+import { isLoggedIn } from "@/hooks/useAuth"
+
+/**
+ * The full-bleed shell. Same frosted sidebar as `_layout`, but the content
+ * region is the whole viewport: the flow editor floats its own chrome over the
+ * canvas instead of sitting inside a padded column.
+ */
+export const Route = createFileRoute("/_canvas")({
+  component: CanvasLayout,
+  beforeLoad: async () => {
+    if (!isLoggedIn()) {
+      throw redirect({ to: "/login" })
+    }
+  },
+})
+
+function CanvasLayout() {
+  return (
+    <SidebarProvider className="bg-card">
+      <AppSidebar />
+      <SidebarInset className="bg-card">
+        <main className="relative h-svh overflow-hidden">
+          <Outlet />
+        </main>
+      </SidebarInset>
+    </SidebarProvider>
+  )
+}
+
+export default CanvasLayout

frontend/src/routes/_canvas/flows/$flowName.tsx

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+import { createFileRoute } from "@tanstack/react-router"
+import { Suspense } from "react"
+
+import { FlowEditor } from "@/components/Flow/FlowEditor"
+import { Skeleton } from "@/components/ui/skeleton"
+
+export const Route = createFileRoute("/_canvas/flows/$flowName")({
+  component: FlowRoute,
+  head: ({ params }) => ({
+    meta: [{ title: `${params.flowName} - Fluksio` }],
+  }),
+})
+
+function Loading() {
+  return (
+    <div className="h-full w-full p-4">
+      <Skeleton className="mx-auto h-10 w-72 rounded-full" />
+    </div>
+  )
+}
+
+function FlowRoute() {
+  const { flowName } = Route.useParams()
+
+  return (
+    <Suspense fallback={<Loading />}>
+      <FlowEditor flowName={flowName} />
+    </Suspense>
+  )
+}

frontend/src/routes/_canvas/flows/index.tsx

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+import {
+  useMutation,
+  useQueryClient,
+  useSuspenseQuery,
+} from "@tanstack/react-query"
+import { createFileRoute, Navigate, useNavigate } from "@tanstack/react-router"
+import { Workflow } from "lucide-react"
+import { Suspense } from "react"
+
+import { FlowsService } from "@/client"
+import { flowKeys, flowsQueryOptions } from "@/components/Flow/queries"
+import { Button } from "@/components/ui/button"
+import { Skeleton } from "@/components/ui/skeleton"
+
+export const Route = createFileRoute("/_canvas/flows/")({
+  component: () => (
+    <Suspense fallback={<Loading />}>
+      <FlowsIndex />
+    </Suspense>
+  ),
+  head: () => ({ meta: [{ title: "Flows - Fluksio" }] }),
+})
+
+function Loading() {
+  return (
+    <div className="flex h-full items-center justify-center">
+      <Skeleton className="h-32 w-64 rounded-lg" />
+    </div>
+  )
+}
+
+function FlowsIndex() {
+  const navigate = useNavigate()
+  const queryClient = useQueryClient()
+  const { data: flows } = useSuspenseQuery(flowsQueryOptions())
+
+  const create = useMutation({
+    mutationFn: () =>
+      FlowsService.saveFlow({
+        name: "my_first_flow",
+        requestBody: { name: "my_first_flow", nodes: [], inputs: [] },
+      }),
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: flowKeys.all })
+      navigate({
+        to: "/flows/$flowName",
+        params: { flowName: "my_first_flow" },
+      })
+    },
+  })
+
+  // With flows around, open the first one rather than showing an empty page.
+  if (flows.data.length > 0) {
+    return (
+      <Navigate
+        to="/flows/$flowName"
+        params={{ flowName: flows.data[0].name }}
+        replace
+      />
+    )
+  }
+
+  return (
+    <div className="flex h-full flex-col items-center justify-center gap-4 px-4 text-center">
+      <span className="flex size-16 items-center justify-center rounded-full bg-muted text-muted-foreground">
+        <Workflow className="size-7" />
+      </span>
+      <div className="grid gap-1">
+        <h1 className="font-display text-lg font-medium">No flows yet</h1>
+        <p className="max-w-sm text-sm text-muted-foreground">
+          A flow is a handful of nodes passing messages to each other. Start
+          with one and add nodes as you go.
+        </p>
+      </div>
+      <Button
+        onClick={() => create.mutate()}
+        disabled={create.isPending}
+        data-testid="create-first-flow"
+      >
+        {create.isPending ? "Creating…" : "Create a flow"}
+      </Button>
+    </div>
+  )
+}