fix(appearance): make Sahara actually differ from Warm light

The sampled colours were Warm light's own (#faf6ea / #e8dfc9 / #ddd2b8) —
the annotated screenshot was that theme, and the request written on it was
"just a little darker". Keep the cream on panels and the entry strip, take
the page, tab bar, toolbars and table headers a shade deeper, and move the
accent from burnt orange to ochre so the two are told apart in the picker.

frontend/src/components/SettingsModal.tsx

@@ -412,7 +412,7 @@ const THEME_SWATCH: Record<Exclude<ThemeChoice, 'auto'>, { bg: string; card: str
   'light-warm':    { bg: '#e8dfc9', card: '#faf6ea', accent: '#b8410c' },
   'light-cool':    { bg: '#f4f6f8', card: '#ffffff', accent: '#2563eb' },
   'light-sage':    { bg: '#eef1ec', card: '#f8faf6', accent: '#2f855a' },
-  'sahara':        { bg: '#e8dfca', card: '#faf6eb', accent: '#b45309' },
+  'sahara':        { bg: '#dcceab', card: '#faf6eb', accent: '#a55f14' },
   'light-nordic':  { bg: '#eef1f7', card: '#ffffff', accent: '#4f46e5' },
   'dim-slate':     { bg: '#343b47', card: '#3d4552', accent: '#fb923c' },
   'dark-warm':     { bg: '#221d18', card: '#2e2820', accent: '#e07a2e' },