feat: design system overhaul — sidebar, AI chats, settings, brainstorm, color cleanup

- Sidebar: dynamic brand-accent colors, brainstorm section restyled
- AI chat general: popup panel with expand/collapse, hides when contextual AI open
- AI chat contextual: tabs reordered (Actions first), X close button, height fix
- Settings: all tabs restyled, 6 new color presets (sage, terracotta, iron, etc.)
- Global color cleanup: emerald/orange hardcoded → brand-accent dynamic
- Brainstorm page: orange → brand-accent throughout
- PageEntry animation component added to key pages
- Floating AI button: bg-brand-accent instead of hardcoded black
- i18n: all 15 locales updated with new AI/billing keys
- Billing: freemium quota tracking, BYOK, stripe subscription scaffolding
- Admin: integrated into new design
- AGENTS.md + CLAUDE.md project rules added

memento-note/app/actions/user-settings.ts

@@ -9,6 +9,7 @@ import { normalizeThemeId, type ThemeId } from '@/lib/apply-document-theme'
 export type UserSettingsData = {
   theme?: ThemeId
   cardSizeMode?: 'variable' | 'uniform'
+  accentColor?: string
 }
 
 /**
@@ -23,9 +24,10 @@ export async function updateUserSettings(settings: UserSettingsData) {
   }
 
   try {
-    const data: { theme?: string; cardSizeMode?: 'variable' | 'uniform' } = {}
+    const data: { theme?: string; cardSizeMode?: 'variable' | 'uniform'; accentColor?: string } = {}
     if (settings.theme !== undefined) data.theme = normalizeThemeId(settings.theme)
     if (settings.cardSizeMode !== undefined) data.cardSizeMode = settings.cardSizeMode
+    if (settings.accentColor !== undefined) data.accentColor = settings.accentColor
 
     await prisma.user.update({
       where: { id: session.user.id },
@@ -38,7 +40,7 @@ export async function updateUserSettings(settings: UserSettingsData) {
     return { success: true }
   } catch (error) {
     console.error('Error updating user settings:', error)
-    throw new Error('Failed to update user settings')
+    throw new Error('Failed to update user settings: ' + (error instanceof Error ? error.message : String(error)))
   }
 }
 
@@ -47,12 +49,13 @@ const getCachedUserSettings = unstable_cache(
     try {
       const user = await prisma.user.findUnique({
         where: { id: userId },
-        select: { theme: true, cardSizeMode: true },
+        select: { theme: true, cardSizeMode: true, accentColor: true },
       })
 
       return {
         theme: normalizeThemeId(user?.theme || 'light'),
         cardSizeMode: (user?.cardSizeMode || 'variable') as 'variable' | 'uniform',
+        accentColor: user?.accentColor || '#A47148',
       }
     } catch (error) {
       console.error('Error getting user settings:', error)
@@ -78,6 +81,7 @@ export async function getUserSettings(userId?: string) {
     return {
       theme: 'light' as const satisfies ThemeId,
       cardSizeMode: 'variable' as const,
+      accentColor: '#A47148',
     }
   }