feat: runtime env

Support runtime environment variables using server components.

This will mean docker images can change env vars for runtime as required.

packages/lib/constants/feature-flags.ts

@@ -1,4 +1,4 @@
-import { APP_BASE_URL } from './app';
+import { appBaseUrl } from './app';
 
 /**
  * The flag name for global session recording feature flag.
@@ -25,7 +25,7 @@ export const LOCAL_FEATURE_FLAGS: Record<string, boolean> = {
  */
 export function extractPostHogConfig(): { key: string; host: string } | null {
   const postHogKey = process.env.NEXT_PUBLIC_POSTHOG_KEY;
-  const postHogHost = `${APP_BASE_URL}/ingest`;
+  const postHogHost = `${appBaseUrl()}/ingest`;
 
   if (!postHogKey || !postHogHost) {
     return null;