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/.env.example

@@ -0,0 +1,34 @@
+# Environment
+ENVIRONMENT=development
+NEXT_PUBLIC_ENV=development
+
+# Site Configuration
+NEXT_PUBLIC_SITE_URL=http://localhost:3000
+
+# Nextauth envs
+# not used in app code but in lib code
+NEXTAUTH_URL=http://localhost:3000
+NEXTAUTH_SECRET=your-nextauth-secret-here
+# / Nextauth envs
+
+# Authentication (Authentik OAuth/OIDC)
+AUTHENTIK_ISSUER=https://authentik.example.com/application/o/reflector
+AUTHENTIK_REFRESH_TOKEN_URL=https://authentik.example.com/application/o/token/
+AUTHENTIK_CLIENT_ID=your-client-id-here
+AUTHENTIK_CLIENT_SECRET=your-client-secret-here
+
+# Feature Flags
+# NEXT_PUBLIC_FEATURE_REQUIRE_LOGIN=true
+# NEXT_PUBLIC_FEATURE_PRIVACY=false
+# NEXT_PUBLIC_FEATURE_BROWSE=true
+# NEXT_PUBLIC_FEATURE_SEND_TO_ZULIP=true
+# NEXT_PUBLIC_FEATURE_ROOMS=true
+
+# API URLs
+NEXT_PUBLIC_API_URL=http://127.0.0.1:1250
+NEXT_PUBLIC_WEBSOCKET_URL=ws://127.0.0.1:1250
+NEXT_PUBLIC_AUTH_CALLBACK_URL=http://localhost:3000/auth-callback
+
+# Sentry
+# SENTRY_DSN=https://your-dsn@sentry.io/project-id
+# SENTRY_IGNORE_API_RESOLUTION_ERROR=1