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/shareZulip.tsx

@@ -1,5 +1,4 @@
 import { useState, useEffect, useMemo } from "react";
-import { featureEnabled } from "../../domainContext";
 import type { components } from "../../reflector-api";
 
 type GetTranscript = components["schemas"]["GetTranscript"];
@@ -25,6 +24,8 @@ import {
   useTranscriptPostToZulip,
 } from "../../lib/apiHooks";
 
+import { featureEnabled } from "../../lib/features";
+
 type ShareZulipProps = {
   transcriptResponse: GetTranscript;
   topicsResponse: GetTranscriptTopic[];