Settings: one window for how far back every graph reaches, 1 minute to 24 hours

Each machine keeps 300 points per curve whatever the window, so memory doesn't follow it;
a wider window means wider points, each the average of its bucket rather than one instant
out of it. The hub passes the setting to every machine it manages.

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

web/src/App.tsx

@@ -4,7 +4,7 @@ import Login from './Login'
 import Shell from './Shell'
 import { Dialogs } from './ui'
 import { applyTheme, currentThemeId } from './themes'
-import { getRefreshMs, setRefreshMs } from './prefs'
+import { getHistorySec, getRefreshMs, setHistorySec, setRefreshMs } from './prefs'
 import { setAccents } from './accents'
 
 export default function App() {
@@ -18,6 +18,9 @@ export default function App() {
         if (p.refreshMs && p.refreshMs !== getRefreshMs()) setRefreshMs(p.refreshMs)
         if (p.accents && typeof p.accents === 'object') setAccents(p.accents, false)
       }).catch(() => { /* keep local */ })
+      // The graph window is the machines' own setting; the copy here only labels the curves
+      // and spaces the live points, so take the hub's word for it at every login.
+      api.historyWindow().then((h) => { if (h.seconds && h.seconds !== getHistorySec()) setHistorySec(h.seconds) }).catch(() => { /* keep local */ })
     } catch (e) { if (e instanceof Unauthenticated) setMe(null) }
   }, [])