Set the pivot theme through restore(), not setAttribute

The previous commit stopped stored layouts overriding the theme, which
was necessary and not sufficient: nothing was setting it either.
setAttribute('theme', ...) does nothing in 5.4.0 -- the theme is a
ViewerConfig field (ViewerConfig.theme, a theme name) and the element
observes no such attribute -- so the pivot stayed light whatever the
toggle said. Presumably it worked on an older Perspective; CLAUDE.md
documented it and is corrected here too.

A partial restore, so it does not rebuild the view the way applyDepth's
whole-config restore does.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CLAUDE.md

@@ -803,7 +803,11 @@ Theme state lives in `ui/src/theme.jsx` — a React context (`ThemeContext`) wit
 - **Toggle:** `setDark(d => !d)` in `StatusBar.jsx`; effect writes `localStorage` and toggles the `.dark` class on `<html>`
 - **CSS:** `ui/src/index.css` defines CSS custom properties under `:root` (light) and `.dark`. All Tailwind color overrides are written as `.dark .bg-white { ... }` etc. — no Tailwind dark-mode config needed
 - **Palette:** dark mode uses Perspective's "Pro Dark" colours (`--bg-primary: #242526`, panels `#2a2c2f`, gridlines `#3b3f46`, text `#c5c9d0`)
-- **Perspective viewer:** `Forecast.jsx` calls `viewer.setAttribute('theme', dark ? 'Pro Dark' : 'Pro Light')` both on initial load and in a `useEffect([dark, versionId])` so the viewer stays in sync when the toggle fires
+- **Perspective viewer:** `Forecast.jsx` calls `viewer.restore({ theme: dark ? 'Pro Dark' : 'Pro Light' })` both on initial load and in a `useEffect([dark, versionId])`. A **partial** restore, so it does not rebuild the view the way `applyDepth`'s whole-config one does.
+
+  It used to be `setAttribute('theme', …)`, which in 5.4.0 does **nothing** — the theme is a `ViewerConfig` field (`ViewerConfig.theme`, a theme *name*), and the element observes no such attribute. The pivot simply stayed light whatever the toggle said.
+
+  Half the fix is in `cleanLayout`, which **drops `theme`**. `viewer.save()` includes it, so every stored layout had one baked in, and restoring one reasserted the author's theme and undid the toggle. It is the reader's choice, not a property of the layout — which also means a published layout cannot impose its theme on whoever applies it. `sameConfig()` ignores `theme` for the same reason: toggling is not a layout edit and must not light the dirty dot.
 - **Consuming the theme:** `import useTheme from '../theme.jsx'` then `const { dark, setDark } = useTheme()`
 
 ## After a change: restart, and Generate SQL

ui/src/views/Forecast.jsx

@@ -449,7 +449,16 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
 
   useEffect(() => {
     if (viewerRef.current) {
-      viewerRef.current.setAttribute('theme', dark ? 'Pro Dark' : 'Pro Light')
+      // restore(), not setAttribute('theme'): the theme is a ViewerConfig field
+      // in 5.4.0 (ViewerConfig.theme, a theme *name* like "Pro Dark"), and the
+      // element observes no such attribute -- the attribute call this replaced
+      // did nothing at all, so the pivot simply stayed light.
+      //
+      // A partial update: everything else is left as it is, so this does not
+      // rebuild the view the way applyDepth's whole-config restore does.
+      // cleanLayout drops `theme` on the way in, so no layout restore puts it
+      // back afterwards.
+      viewerRef.current.restore({ theme: dark ? 'Pro Dark' : 'Pro Light' })
     }
   }, [dark, versionId])
 
@@ -923,7 +932,7 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
         console.error('[setAutoPause]', err)
       }
 
-      viewer.setAttribute('theme', dark ? 'Pro Dark' : 'Pro Light')
+      await viewer.restore({ theme: dark ? 'Pro Dark' : 'Pro Light' })
       if (!hideSplitTotal()) setTimeout(hideSplitTotal, 400)
 
       // restore last-used layout or build default