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/is-stream/index.js

@@ -0,0 +1,29 @@
+export function isStream(stream) {
+	return stream !== null
+		&& typeof stream === 'object'
+		&& typeof stream.pipe === 'function';
+}
+
+export function isWritableStream(stream) {
+	return isStream(stream)
+		&& stream.writable !== false
+		&& typeof stream._write === 'function'
+		&& typeof stream._writableState === 'object';
+}
+
+export function isReadableStream(stream) {
+	return isStream(stream)
+		&& stream.readable !== false
+		&& typeof stream._read === 'function'
+		&& typeof stream._readableState === 'object';
+}
+
+export function isDuplexStream(stream) {
+	return isWritableStream(stream)
+		&& isReadableStream(stream);
+}
+
+export function isTransformStream(stream) {
+	return isDuplexStream(stream)
+		&& typeof stream._transform === 'function';
+}