fix(sales-orders): pin the sales_order_items embed FK and teach the embed guard composite keys (#2207)

* fix(sales-orders): pin the sales_order_items embed FK and teach the embed guard composite keys

Migration 20260902180000_sales_orders_hardening added a composite
(sales_order_id, company_id) foreign key from sales_order_items to
sales_orders next to the original single-column one. PostgREST then saw
two relationships and answered every `items:sales_order_items(*)` embed
with HTTP 300 / PGRST201, so kundorder list, detail, create and the MCP
list tool all failed on prod and staging with "Oväntat serverfel".

- Hint the three embeds with `!sales_order_items_sales_order_id_fkey`
  (route, load service, MCP list tool).
- scripts/checks/ambiguous-embed.mjs only parsed single-column
  `FOREIGN KEY (col)`, which is why the ratchet reported 0 for this pair.
  It now reads composite column lists (named or default constraint
  name) in both CREATE TABLE and ALTER TABLE, derives the same 17
  ambiguous pairs prod's pg_constraint reports, and flags all three
  shipped sites on main.
- Unit tests for the composite shapes: alongside a single-column key,
  replacing one, and inline in CREATE TABLE.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Q7xJQL2aZo6iRHxCZNntUq

* fix(checks): drop composite embed edges when DROP COLUMN removes a member column

Postgres drops every foreign key a column takes part in, so the
ambiguous-embed parser must release a composite edge (and its constraint
name) when one of its columns is dropped, not only the single-column key.
Otherwise a later migration would keep a pair armed for a relationship
that no longer exists and reject valid embeds. Regression case added.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Q7xJQL2aZo6iRHxCZNntUq

---------

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

lib/sales-orders/load.ts

@@ -35,7 +35,7 @@ export async function loadSalesOrder(
 ): Promise<ServiceResult<{ order: SalesOrder }>> {
   const { data, error } = await supabase
     .from('sales_orders')
-    .select('*, customer:customers(*), items:sales_order_items(*)')
+    .select('*, customer:customers(*), items:sales_order_items!sales_order_items_sales_order_id_fkey(*)')
     .eq('id', orderId)
     .eq('company_id', companyId)
     .maybeSingle()