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/pino-pretty/lib/utils/is-valid-date.js

@@ -0,0 +1,14 @@
+'use strict'
+
+module.exports = isValidDate
+
+/**
+ * Checks if the argument is a JS Date and not 'Invalid Date'.
+ *
+ * @param {Date} date The date to check.
+ *
+ * @returns {boolean} true if the argument is a JS Date and not 'Invalid Date'.
+ */
+function isValidDate (date) {
+  return date instanceof Date && !Number.isNaN(date.getTime())
+}