dev-api: add developer portal, OpenAPI spec, and Flatenbadet case study

- New /developers/ page with API docs, SDKs, pricing, use cases
- OpenAPI 3.0 spec for Orders, Missions, Photos, Analytics
- Case study: Glasskiosken i Flatenbadet — complete ROI analysis
- Updated /order/ with recurring missions and frequency dropdown

services/frilans-payout/node_modules/postgres-interval/index.d.ts

@@ -0,0 +1,20 @@
+declare namespace PostgresInterval {
+  export interface IPostgresInterval {
+    years?: number;
+    months?: number;
+    days?: number;
+    hours?: number;
+    minutes?: number;
+    seconds?: number;
+    milliseconds?: number;
+
+    toPostgres(): string;
+
+    toISO(): string;
+    toISOString(): string;
+  }
+}
+
+declare function PostgresInterval(raw: string): PostgresInterval.IPostgresInterval;
+
+export = PostgresInterval;