fix(portal): workflows layout — canvas collapsed to 0 width

The workflows route layout used `display: flex` on the wrapper without
giving the `.flow` child `flex: 1`. With Flexbox's default
`flex: 0 1 auto`, the child shrunk to its non-flex content — palette
(234px) + inspector (286px) = 520px — leaving the canvas wrap at width 0.
Nodes, toolbar and zoom controls were positioned absolutely against a
0-wide parent so nothing painted.

Fix: drop `display: flex` on the wrapper. `.flow` already has
`display: flex; height: 100%` and as a block-level child it fills the
width naturally.

Verified via Playwright: canvas-wrap now 1168×746 and all 7 seed nodes
render at expected positions.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/app/[slug]/workflows/layout.tsx

@@ -2,16 +2,18 @@ import type { ReactNode } from "react";
 
 // Workflows is full-bleed — the editor (palette + canvas + inspector)
 // takes the entire content area, so we strip the standard `.content-inner`
-// max-width wrapper. The parent `.content` is already `overflow-y: auto`,
-// so we force `min-height: 0` here to let the editor's own grid fill.
+// max-width wrapper and pin a block container that `.flow` (display:flex,
+// height:100%) fills naturally.
+//
+// Don't make this wrapper `display: flex` — the child `.flow` would then
+// be a non-flex flex-item that shrinks to its fixed-width palette +
+// inspector and leaves the canvas at width 0.
 export default function WorkflowsLayout({ children }: { children: ReactNode }) {
   return (
     <div
       style={{
         position: "absolute",
         inset: 0,
-        display: "flex",
-        minHeight: 0,
         overflow: "hidden",
       }}
     >