Bug: enable_signup=false disables entire email/phone provider instead of just signups

# Correction I need to correct my initial understanding after feedback: ## The Actual Behavior These variables control the **entire authentication provider**, not just signup: - `ENABLE_EMAIL_SIGNUP` → `GOTRUE_EXTERNAL_EMAIL_ENABLED` - `ENABLE_PHONE_SIGNUP` → `GOTRUE_EXTERNAL_PHONE_ENABLED` - `DISABLE_SIGNUP` → `GOTRUE_DISABLE_SIGNUP` (global flag) ## Invite-Only Configuration **Docker:** ```env DISABLE_SIGNUP=true ENABLE_EMAIL_SIGNUP=true ENABLE_PHONE_SIGNUP=true ``` **CLI:** ```toml [auth] enable_signup = false [auth.email] enable_signup = true [auth.sms] enable_signup = true ``` ## Proposed change Not a bug - documentation clarity issue. Fixed in #40575 and supabase/cli#4469 by adding detailed comments explaining provider vs signup control, # Original Report: ## Bug report - [x] I confirm this is a bug with Supabase, not with my own application. - [x] I confirm I have searched the [Docs](https://docs.supabase.com), GitHub [Discussions](https://github.com/supabase/supabase/discussions), and [Discord](https://discord.supabase.com). ## Describe the bug Setting `[auth.email].enable_signup = false` disables the entire email provider instead of just preventing signups, breaking invite-only authentication. Same issue affects `[auth.sms].enable_signup`. **Error:** `422 {"msg":"email_provider_disabled"}` ## To Reproduce **CLI:** ```toml [auth.email] enable_signup = false ``` **Docker:** ```env ENABLE_EMAIL_SIGNUP=false ``` Attempt to send a magic link or authenticate an invited user → provider disabled error. ## Expected behavior Should only disable signups while allowing invited users to authenticate via email/password/OTP. ## System information - **Affects:** - Supabase CLI v1.0.0+ (since [d347621](https://github.com/supabase/cli/commit/d3476211983b9740cc46eb3979c971bb63195af2), Feb 2022) - Docker Compose (since [0e036d4](https://github.com/supabase/supabase/commit/0e036d494839e539661bd06581db47c7f4b36b0c), Sept 2021) - **Observed with:** Supabase CLI latest, Docke…