chore: small onboarding docs/DX updates (#47719)

## I have read the
[CONTRIBUTING.md](https://github.com/supabase/supabase/blob/master/CONTRIBUTING.md)
file.

YES (in fact, this PR makes a tiny change!)

## What kind of change does this PR introduce?

Docs and config file changes to fix up some outdated docs and improve
the onboarding experience a little bit:

- [x] Fixes up the `pnpm` versioning guidance in `DEVELOPERS.md` (as
well as some small formatting cleanups)
- [x] Introduces a lightweight `mise.toml` file for
[mise](https://mise.en.dev/) users. We use mise in other codebases in
the @supabase org — if you have mise installed and you open your
terminal into this codebase, mise will read the `mise.toml` file and
automatically set up the Node/pnpm versions set in the
`.nvmrc`/`package.json` files.
- [x] Cleans up a TOC in `CONTRIBUTING.md` that looked ill-formatted —
the numbered list appears on one line, which I don't believe is intended
(see
[here](https://github.com/supabase/supabase/blob/561e43b36c02cb5576e7ea3d3a11f9349ace0bcc/CONTRIBUTING.md)).
I opted to remove the TOC wholesale as opposed to fixing the formatting
since the GitHub UI has a native TOC viewer.


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Documentation**
* Updated contributor and developer guides to improve navigation and
clarify setup instructions.
  * Removed an extra table of contents from the contributing guide.
* Refined dependency/version guidance and formatting in the development
guide.
* **Chores**
* Updated local tooling settings to better support version-file based
workflows.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

CONTRIBUTING.md

@@ -2,10 +2,6 @@
 
 Thank you for contributing to Supabase! We’re a big, exciting open source project and we’d love to have you contribute! Here’s some resources and guidance to help you get started:
 
-[1. Getting Started](#getting-started)
-[2. Issues](#issues)
-[3. Pull Requests](#pull-requests)
-
 ## Getting Started
 
 To ensure a positive and inclusive environment, please read our [code of conduct](https://github.com/supabase/.github/blob/main/CODE_OF_CONDUCT.md) before contributing. For help setting up the code in this repo, please follow our [DEVELOPERS.md](https://github.com/supabase/supabase/blob/master/DEVELOPERS.md) file. For the [docs](https://supabase.com/docs) site, follow this [CONTRIBUTING.md](https://github.com/supabase/supabase/blob/master/apps/docs/CONTRIBUTING.md) guide.

DEVELOPERS.md

@@ -1,7 +1,6 @@
 # Developing Supabase
 
 - [Developing Supabase](#developing-supabase)
-
   - [Getting started](#getting-started)
     - [Install dependencies](#install-dependencies)
   - [Local development](#local-development)
@@ -34,11 +33,11 @@ To ensure a positive and inclusive environment, please read our [code of conduct
 
 You will need to install and configure the following dependencies on your machine to build [Supabase](https://supabase.com):
 
-- [Git](https://git-scm.com/)
-- [Node.js](https://nodejs.org) version as documented in [.nvmrc](./.nvmrc)
-- [pnpm](https://pnpm.io/) version 9.x.x or higher
-- [make](https://www.gnu.org/software/make/) or the equivalent to `build-essentials` for your OS
-- [Docker](https://docs.docker.com/get-docker/) (to run studio locally)
+- [**Git**](https://git-scm.com/)
+- [**Node.js**](https://nodejs.org) (version as documented in [`.nvmrc`](./.nvmrc))
+- [**pnpm**](https://pnpm.io/) (version as documented in the `packageManager` field in [`package.json`](./package.json))
+- [**make**](https://www.gnu.org/software/make/) (or the equivalent to `build-essentials` for your OS)
+- [**Docker**](https://docs.docker.com/get-docker/) (to run studio locally)
 
 ## Local development
 
@@ -120,7 +119,6 @@ For example:
 1. `cd apps/studio`: move to the `studio` workspace.
 2. `pnpm add react`: installs `react` into `studio` workspace.
 
-
 ---
 
 ## Running Docker for Supabase Studio

mise.toml

@@ -0,0 +1,2 @@
+[settings]
+idiomatic_version_file_enable_tools = ["node", "pnpm"]