## What kind of change does this PR introduce?
Feature
## What is the current behavior?
Functions page on self-hosted differs from Platform
## What is the new behavior?
> [!NOTE]
> This PR only add readonly operations. Function edit and deploy should
be implemented in a future one.
Adds the possibility to download and see function code in Self-Host
version.
<details>
<img width="1465" height="944" alt="image"
src="https://github.com/user-attachments/assets/4bbf8f5c-3390-4de6-9e8b-8ec9cd59ebad"
/>
</details>
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **New Features**
* API endpoint to stream function files/artifacts as
multipart/form-data.
* New function file entry type and server-side file listing for
functions.
* **Improvements**
* Edge Functions "Code" navigation item always visible.
* Download popover reworked: ZIP download always available; CLI section
shown only on supported platforms.
* Editor set to read-only and file actions disabled on unsupported
environments.
* **Editor**
* Added JavaScript, TypeScript, and Markdown language modules for the
embedded editor.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
---------
Co-authored-by: Charis Lam <26616127+charislam@users.noreply.github.com>
