feat: replace nextjs-config with environment variables (#632)

* chore: remove nextjs-config

* build fix

* update readme

* explicit nextjs env vars + remove feature-unrelated things and obsolete vars from config

* full config removal

* remove force-dynamic from pages

* compile fix

* restore claude-deleted tests

* better .env.example

---------

Co-authored-by: Igor Loskutov <igor.loskutoff@gmail.com>

www/app/(app)/transcripts/shareAndPrivacy.tsx

@@ -1,5 +1,4 @@
 import { useEffect, useState } from "react";
-import { featureEnabled } from "../../domainContext";
 
 import { ShareMode, toShareMode } from "../../lib/shareMode";
 import type { components } from "../../reflector-api";
@@ -24,6 +23,8 @@ import ShareCopy from "./shareCopy";
 import ShareZulip from "./shareZulip";
 import { useAuth } from "../../lib/AuthProvider";
 
+import { featureEnabled } from "../../lib/features";
+
 type ShareAndPrivacyProps = {
   finalSummaryRef: any;
   transcriptResponse: GetTranscript;