feat(zettle): sync paid purchases into webshop_orders (#2445)

Community PR #2416 by @olofpinzke, adopted and finished by maintainers (rebased so every commit is signed).

Why the problem occurred: no Zettle integration; POS sales only reached the books as bank descriptors while Woo/Shopify already had order underlag via webshop_orders. The contributor's version also failed at the database (platform CHECKs listed only woocommerce/shopify), which the mocked unit tests never saw.
What was simplified: reused the Orders/book/invoice path instead of a new inbox; Finance API payouts/fees deferred. Sales the one-account, revenue-per-rate model cannot book (split tender, gift cards, tips) import unbookable with a "bokför manuellt" title instead of guessing accounts. Reset parity uses the rename-and-wrap pattern instead of re-issuing the reset body.
Why this solution: per-purchase rows give the radunderlag BFL verifikat need and the bulk-book path exists; daily kassarapport aggregation and Finance API fees/payouts are the follow-up (DECISIONS.md). Skeptic-refuted paths fixed before merge: concurrent refresh-token rotation (sync claim), cron offset paging (candidate snapshot), platform CHECKs, writer-role gate, migration-reset parity, white-label return origin re-validated at callback, VAT net from product rows.

Not live until ZETTLE_CLIENT_ID / ZETTLE_CLIENT_SECRET / ZETTLE_CREDENTIALS_ENCRYPTION_KEY are set on Vercel and a Zettle developer app is registered with the callback redirect URI.

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WtYqzKPoTSRHskYYdf7MwB

lib/dashboard/__tests__/nav-flags.test.ts

@@ -70,6 +70,7 @@ describe('getDashboardNavFlags', () => {
       'shopify_connections',
       'webshop_orders',
       'woocommerce_connections',
+      'zettle_connections',
     ])
   })
 

lib/dashboard/nav-flags.ts

@@ -70,15 +70,19 @@ export async function getDashboardNavFlagsViaProbes(
   supabase: SupabaseClient,
   companyId: string,
 ): Promise<Omit<DashboardNavFlags, 'hasExpenseClaims'>> {
-  const [woo, shopify, orders, trips] = await Promise.all([
+  const [woo, shopify, zettle, orders, trips] = await Promise.all([
     supabase.from('woocommerce_connections').select('id').eq('company_id', companyId).eq('status', 'active').limit(1),
     supabase.from('shopify_connections').select('id').eq('company_id', companyId).eq('status', 'active').limit(1),
+    supabase.from('zettle_connections').select('id').eq('company_id', companyId).eq('status', 'active').limit(1),
     supabase.from('webshop_orders').select('id').eq('company_id', companyId).limit(1),
     supabase.from('mileage_trips').select('id').eq('company_id', companyId).limit(1),
   ])
   return {
     hasWebshop:
-      (woo.data?.length ?? 0) > 0 || (shopify.data?.length ?? 0) > 0 || (orders.data?.length ?? 0) > 0,
+      (woo.data?.length ?? 0) > 0 ||
+      (shopify.data?.length ?? 0) > 0 ||
+      (zettle.data?.length ?? 0) > 0 ||
+      (orders.data?.length ?? 0) > 0,
     hasMileageTrips: (trips.data?.length ?? 0) > 0,
   }
 }