web: three panels — Generate, Gallery, Collections — and a layout

ported from the standalone app's hash-tab UI. The panels do not coordinate through props (the panel
contract only ever hands a component its panelId) or usePanelChannel-as-selection:

- Gallery's lightbox is ?selected=<id>, Collections' detail is ?collection=<id> — different names
  since both panels render on the same route at once
- Generate bumps useAtelierRefresh (added to officerdev/src/channels.ts) when a job finishes;
  Gallery subscribes to it — a genuine signal, not a selection, so it stays a channel

images render through GET /files/:filename with a ?token= query param appended client-side
(lib/api.ts's fileUrl), the same escape hatch FileViewer and the music plugin use for exactly this:
a browser cannot set an Authorization header on an <img src>.

Providers is not here — see PLUGIN.md for why it became a platform settings screen instead.

assets/icon.png and assets/splash.png are [placeholder] flat swatches, not real artwork — see
assets/PLACEHOLDER.md.

web/layout.ts

@@ -0,0 +1,15 @@
+import type { LayoutNode } from 'officerdev';
+
+// Generate stays narrow and fixed — it is a form, not a working area. Gallery gets the most room: it
+// is the main "what did I make" view. Collections is the organising view, smallest of the three. Users
+// can resize or rearrange freely; this is only the starting point.
+export const defaultLayout: LayoutNode = {
+  type: 'group',
+  id: 'atelier-root',
+  direction: 'horizontal',
+  children: [
+    { node: { type: 'panel', id: 'atelier-generate', appType: 'atelier-generate' }, size: 26 },
+    { node: { type: 'panel', id: 'atelier-gallery', appType: 'atelier-gallery' }, size: 48 },
+    { node: { type: 'panel', id: 'atelier-collections', appType: 'atelier-collections' }, size: 26 },
+  ],
+};