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/shareLink.tsx

@@ -1,8 +1,9 @@
 import React, { useState, useRef, useEffect, use } from "react";
-import { featureEnabled } from "../../domainContext";
 import { Button, Flex, Input, Text } from "@chakra-ui/react";
 import QRCode from "react-qr-code";
 
+import { featureEnabled } from "../../lib/features";
+
 type ShareLinkProps = {
   transcriptId: string;
 };