Add tenant branding & theming system with admin UI

Tenant admins can now customize their workspace appearance: page/nav
backgrounds (solid, gradient, or image), column/card colors, borders,
text, opacity with glass blur, card corner radius, and accent colors.
Light and dark mode are configured separately. Theme CSS is injected
server-side via transformPageChunk to prevent FOUC.

Includes avatar components, account page updates, and pre-existing
type error fixes (Buffer, async onMount, InputJsonValue).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

prisma/schema.prisma

@@ -22,6 +22,7 @@ model Tenant {
   tags           Tag[]
   categories     Category[]
   boardTemplates BoardTemplate[]
+  theme          TenantTheme?
 
   @@map("tenants")
 }
@@ -329,3 +330,59 @@ model BoardTemplate {
 
   @@map("board_templates")
 }
+
+// ─── Tenant Branding & Theming ───────────────────────────────
+
+model TenantTheme {
+  id       String @id @default(uuid()) @db.Uuid
+  tenantId String @unique @map("tenant_id") @db.Uuid
+
+  // Light mode
+  lightPageBg        String? @map("light_page_bg")
+  lightPageBgImage   String? @map("light_page_bg_image")
+  lightNavBg         String? @map("light_nav_bg")
+  lightNavBgImage    String? @map("light_nav_bg_image")
+  lightColumnBg      String? @map("light_column_bg")
+  lightColumnBorder  String? @map("light_column_border")
+  lightColumnText    String? @map("light_column_text")
+  lightColumnOpacity Float?  @map("light_column_opacity")
+  lightCardBg        String? @map("light_card_bg")
+  lightCardBorder    String? @map("light_card_border")
+  lightCardText      String? @map("light_card_text")
+  lightCardOpacity   Float?  @map("light_card_opacity")
+  lightCardRadius    String? @map("light_card_radius")
+  lightPrimary       String? @map("light_primary")
+  lightPrimaryHover  String? @map("light_primary_hover")
+  lightDanger        String? @map("light_danger")
+  lightDangerHover   String? @map("light_danger_hover")
+  lightSuccess       String? @map("light_success")
+  lightWarning       String? @map("light_warning")
+
+  // Dark mode
+  darkPageBg        String? @map("dark_page_bg")
+  darkPageBgImage   String? @map("dark_page_bg_image")
+  darkNavBg         String? @map("dark_nav_bg")
+  darkNavBgImage    String? @map("dark_nav_bg_image")
+  darkColumnBg      String? @map("dark_column_bg")
+  darkColumnBorder  String? @map("dark_column_border")
+  darkColumnText    String? @map("dark_column_text")
+  darkColumnOpacity Float?  @map("dark_column_opacity")
+  darkCardBg        String? @map("dark_card_bg")
+  darkCardBorder    String? @map("dark_card_border")
+  darkCardText      String? @map("dark_card_text")
+  darkCardOpacity   Float?  @map("dark_card_opacity")
+  darkCardRadius    String? @map("dark_card_radius")
+  darkPrimary       String? @map("dark_primary")
+  darkPrimaryHover  String? @map("dark_primary_hover")
+  darkDanger        String? @map("dark_danger")
+  darkDangerHover   String? @map("dark_danger_hover")
+  darkSuccess       String? @map("dark_success")
+  darkWarning       String? @map("dark_warning")
+
+  createdAt DateTime @default(now()) @map("created_at")
+  updatedAt DateTime @updatedAt @map("updated_at")
+
+  tenant Tenant @relation(fields: [tenantId], references: [id], onDelete: Cascade)
+
+  @@map("tenant_themes")
+}