feat: add command palette, accessibility, scroll animations, demo workspace, and keyboard navigation

- COMP-139: Command palette for quick navigation
- COMP-140: Accessibility improvements
- COMP-141: Scroll animations with animate-on-scroll component
- COMP-143: Demo workspace with seed data and demo banner
- COMP-145: Keyboard navigation and shortcuts help

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-Claude)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

packages/database/prisma/schema.prisma

@@ -15,6 +15,7 @@ model User {
   passwordHash  String
   name          String?
   emailVerified Boolean  @default(false)
+  demoSeeded    Boolean  @default(false)
 
   createdAt     DateTime @default(now())
   updatedAt     DateTime @updatedAt
@@ -124,7 +125,8 @@ model Trace {
   tags        String[] @default([])
   metadata    Json?
 
-  // Owner — nullable for backward compat with existing unowned traces
+  isDemo      Boolean  @default(false)
+
   userId      String?
   user        User?    @relation(fields: [userId], references: [id], onDelete: SetNull)