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/extensions/_generated/enabled-extensions.ts

@@ -15,5 +15,6 @@ export const ENABLED_EXTENSION_IDS: ReadonlySet<string> = new Set([
   'whatsapp-inbox',
   'woocommerce',
   'shopify',
+  'zettle',
   'mail',
 ])

lib/extensions/_generated/extension-list.ts

@@ -14,6 +14,7 @@ import { stripeExtension } from '@/extensions/general/stripe'
 import { whatsappInboxExtension } from '@/extensions/general/whatsapp-inbox'
 import { woocommerceExtension } from '@/extensions/general/woocommerce'
 import { shopifyExtension } from '@/extensions/general/shopify'
+import { zettleExtension } from '@/extensions/general/zettle'
 import { mailExtension } from '@/extensions/general/mail'
 
 export const FIRST_PARTY_EXTENSIONS: Extension[] = [
@@ -31,5 +32,6 @@ export const FIRST_PARTY_EXTENSIONS: Extension[] = [
   whatsappInboxExtension,
   woocommerceExtension,
   shopifyExtension,
+  zettleExtension,
   mailExtension,
 ]

lib/extensions/_generated/sector-definitions.ts

@@ -184,6 +184,17 @@ export const EXTENSION_DEFINITIONS: Record<string, ExtensionDefinition[]> = {
           "longDescription": "Anslut din Shopify-butik så hämtas betalda ordrar och återbetalningar automatiskt varje natt till Ordersidan, med belopp, betalsätt och moms per sats. Inget bokförs automatiskt: du bokför varje order själv från Ordersidan.",
           "hasOwnData": true
     },
+    {
+          "slug": "zettle",
+          "name": "Zettle",
+          "sector": "general",
+          "category": "import",
+          "icon": "CreditCard",
+          "dataPattern": "manual",
+          "description": "Hämta betalda köp och återbetalningar från Zettle till Ordersidan",
+          "longDescription": "Anslut ditt Zettle-konto så hämtas betalda köp och återbetalningar automatiskt varje natt till Ordersidan, med belopp, betalsätt, moms per sats och radunderlag. Inget bokförs automatiskt: du bokför varje köp själv från Ordersidan.",
+          "hasOwnData": true
+    },
     {
           "slug": "mail",
           "name": "Brevlådor",