Unify brand background to #121212, remove divider under Layout tiles

- All 4 brands' bg.primary now use the same #121212 (was a slightly
  different near-black per brand) — verified via pixel sampling of
  rendered OG images
- Content group no longer has a top divider, removing the line that sat
  directly under the Layout tiles (same noDivider pattern used for Layout
  itself against the Format buttons above it)

apps/og-generator/app/page.tsx

@@ -774,7 +774,7 @@ export default function Page() {
             </Group>
           )}
 
-          <Group title="Content">
+          <Group title="Content" noDivider>
             {showOg && (
               <div className="flex flex-col gap-2">
                 <label htmlFor="eyebrow" className="text-sm font-medium text-foreground-light">

apps/og-generator/lib/design/brands/multigres.ts

@@ -14,7 +14,7 @@ export const multigres: Brand = {
   id: 'multigres',
   name: 'Multigres',
   colorPalette: {
-    'bg.primary': '#15161C',
+    'bg.primary': '#121212',
     'bg.alt': '#111218',
     'surface.100': '#22242E',
     'surface.200': '#262833',

apps/og-generator/lib/design/brands/oriole.ts

@@ -14,7 +14,7 @@ export const oriole: Brand = {
   id: 'oriole',
   name: 'Oriole',
   colorPalette: {
-    'bg.primary': '#1A1512',
+    'bg.primary': '#121212',
     'bg.alt': '#15110E',
     'surface.100': '#2A231D',
     'surface.200': '#2E2620',

apps/og-generator/lib/design/brands/supabase.ts

@@ -10,7 +10,7 @@ export const supabase: Brand = {
   id: 'supabase',
   name: 'Supabase',
   colorPalette: {
-    'bg.primary': '#1C1C1C',
+    'bg.primary': '#121212',
     'bg.alt': '#171717',
     'surface.100': '#2A2A2A',
     'surface.200': '#2E2E2E',

apps/og-generator/lib/design/brands/supasquad.ts

@@ -14,7 +14,7 @@ export const supasquad: Brand = {
   id: 'supasquad',
   name: 'Supasquad',
   colorPalette: {
-    'bg.primary': '#160F1C',
+    'bg.primary': '#121212',
     'bg.alt': '#120C17',
     'surface.100': '#241A2C',
     'surface.200': '#291E32',