feat(web): Schedule-First redesign

- Top header bar + narrow sidebar layout
- Dashboard: calendar-style schedule with timeline cards
- Clients: card-based layout with avatar initials and pet count
- Services: grid cards with emoji indicators and pricing
- Bookings: timeline cards with time slots, status chips, inline actions
- Invoices: cards with status badges, action buttons
- All pages: search bars, empty states, modal forms
- Consistent color system: indigo primary, amber alerts, gray hierarchy

api/prisma/schema.prisma

@@ -98,7 +98,7 @@ model Booking {
   priceOverride Float?
   petId         String?
   pet           Pet?      @relation("PetBookings", fields: [petId], references: [id])
-  invoice       Invoice?  @relation(references: [id])
+  invoice       Invoice?  @relation()
   recurringRule Json?
 
   @@map("bookings")
@@ -128,7 +128,7 @@ model Invoice {
   clientId    String
   client      Client       @relation(fields: [clientId], references: [id])
   bookingId   String?      @unique
-  booking     Booking?     @relation(references: [id])
+  booking     Booking?     @relation(fields: [bookingId], references: [id])
   invoiceItems InvoiceItem[]
 
   @@map("invoices")