Add product catalog and quote builder improvements

[jusso-dev]

Context

ScopeStack supports document line items, pricing modes, tax, discounts, payment terms, and Xero invoicing. PandaDoc-style tools go further with quote builders, catalogs, optional add-ons, and CRM/product-data driven pricing.

Goal

Build a product/service catalog and stronger quote builder experience for reusable pricing and optional client choices.

Scope

• Add product/service catalog items.
• Support default unit price, tax rate, billing frequency, description, SKU/code, and category.
• Allow adding catalog items to document line items.
• Support optional add-ons in a quote.
• Support quote variants/options for client selection where appropriate.
• Add discount/margin guardrails or approval hooks as a later stage.
• Keep Xero invoice generation compatible with catalog-backed line items.

UX Notes

• In the document editor, adding a line item should allow searching the catalog.
• Users should still be able to create ad hoc line items.
• Optional add-ons should be clear in the client-facing document.
• Avoid overbuilding CPQ rules in v1. Start with reusable catalog items and optional choices.

Data/Architecture Notes

Potential models:

• CatalogItem
  • organisationId
  • name
  • description
  • sku
  • category
  • unitPrice
  • taxRate
  • billingFrequency
  • active
• Extend DocumentLineItem with optional catalogItemId, isOptional, selectedByClient.

Acceptance Criteria

• Users can manage catalog items.
• Users can add catalog items to documents.
• Ad hoc line items still work.
• Optional add-ons can be shown and selected/confirmed before acceptance.
• Totals correctly reflect selected required and optional items.
• Xero invoice creation handles catalog-backed line items.
• Tests cover totals, optional items, and Xero payload compatibility.

Dependencies

• Payments issue may depend on final accepted totals.
• Client portal UX will need to show optional selections clearly.

Priority

P1. Important for PandaDoc-style proposal value and faster quote creation.