Refactor environment files and update .gitignore

Environment variable definitions were moved from .env.development, .env.test and .env.production to a new shared .env file. This provides a centralized location for common environment variables values, easier manageability, and overrides capability in specific environments. The .gitignore file was also updated to no longer ignore the .env file as this file now contains public / non-sensitive configuration values.

apps/web/.env.production

@@ -1,51 +1,16 @@
+# PRODUCTION ENVIRONMENT VARIABLES
+
 ## DO NOT ADD VARS HERE UNLESS THEY ARE PUBLIC OR NOT SENSITIVE
 ## THIS ENV IS USED FOR PRODUCTION AND IS COMMITED TO THE REPO
 ## AVOID PLACING SENSITIVE DATA IN THIS FILE.
 ## PUBLIC KEYS OR CONFIGURATION ARE OKAY TO BE PLACED HERE.
 
-# SITE
-NEXT_PUBLIC_SITE_URL=http://localhost:3000
-NEXT_PUBLIC_PRODUCT_NAME=Makerkit
-NEXT_PUBLIC_SITE_TITLE="Makerkit - The easiest way to build and manage your SaaS"
-NEXT_PUBLIC_SITE_DESCRIPTION="Makerkit is the easiest way to build and manage your SaaS. It provides you with the tools you need to build your SaaS, without the hassle of building it from scratch."
-NEXT_PUBLIC_DEFAULT_THEME_MODE=light
-NEXT_PUBLIC_THEME_COLOR="#ffffff"
-NEXT_PUBLIC_THEME_COLOR_DARK="#0a0a0a"
-
-# LOCALES PATH
-NEXT_PUBLIC_LOCALES_PATH=apps/web/public/locales
-
-# PATHS (to be used in "packaages")
-SIGN_IN_PATH=/auth/sign-in
-SIGN_UP_PATH=/auth/sign-up
-TEAM_ACCOUNTS_HOME_PATH=/home
-INVITATION_PAGE_PATH=/join
-
-# CMS
-CMS_CLIENT=keystatic
-
-# KEYSTATIC
-NEXT_PUBLIC_KEYSTATIC_CONTENT_PATH=./content
-
-# AUTH
-NEXT_PUBLIC_AUTH_PASSWORD=true
-NEXT_PUBLIC_AUTH_MAGIC_LINK=false
-
-# BILLING
-NEXT_PUBLIC_BILLING_PROVIDER=stripe
-
 # SUPABASE
 NEXT_PUBLIC_SUPABASE_URL=
 
 # STRIPE
 NEXT_PUBLIC_STRIPE_PUBLISHABLE_KEY=
 
-# FEATURE FLAGS
-NEXT_PUBLIC_ENABLE_ACCOUNT_DELETION=true
-NEXT_PUBLIC_ENABLE_PERSONAL_ACCOUNT_BILLING=true
-NEXT_PUBLIC_ENABLE_ORGANIZATION_DELETION=true
-NEXT_PUBLIC_ENABLE_ORGANIZATION_BILLING=true
-
 # MONITORING
 MONITORING_PROVIDER=
 MONITORING_INSTRUMENTATION_ENABLED=false