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/path-exists/index.d.ts

@@ -0,0 +1,28 @@
+declare const pathExists: {
+	/**
+	Check if a path exists.
+
+	@returns Whether the path exists.
+
+	@example
+	```
+	// foo.ts
+	import pathExists = require('path-exists');
+
+	(async () => {
+		console.log(await pathExists('foo.ts'));
+		//=> true
+	})();
+	```
+	*/
+	(path: string): Promise<boolean>;
+
+	/**
+	Synchronously check if a path exists.
+
+	@returns Whether the path exists.
+	*/
+	sync(path: string): boolean;
+};
+
+export = pathExists;