Unify invoices and quotes UI with discount, tax, and credit notes.

Match list/form mockups on desktop and mobile, wire real APIs for billing fields, and merge proforma into the invoices section.

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/api/prisma/schema.prisma

@@ -614,6 +614,9 @@ model Quote {
   status         QuoteStatus     @default(draft)
   currency       String          @default("IRR")
   notes          String?
+  discountAmount Decimal         @default(0) @db.Decimal(18, 2)
+  taxPercent     Decimal         @default(0) @db.Decimal(8, 2)
+  issuedAt       DateTime?
   validUntil     DateTime?
   personId       String?
   person         Person?         @relation(fields: [personId], references: [id], onDelete: SetNull)
@@ -661,8 +664,11 @@ model Invoice {
   number         String
   title          String
   status         InvoiceStatus        @default(draft)
+  kind           String               @default("invoice") // invoice | credit
   currency       String               @default("IRR")
   notes          String?
+  discountAmount Decimal              @default(0) @db.Decimal(18, 2)
+  taxPercent     Decimal              @default(0) @db.Decimal(8, 2)
   issuedAt       DateTime?
   dueDate        DateTime?
   personId       String?