docs: update EdgeDB references to Gel rebrand (#24487)

## Summary
EdgeDB has rebranded to Gel. This PR comprehensively updates all
documentation to reflect the rebrand.

## Changes Made

### Documentation & Branding
- **Guide title**: "Use EdgeDB with Bun" → "Use Gel with Bun"
- **File renamed**: `docs/guides/ecosystem/edgedb.mdx` → `gel.mdx`
- **Description**: Added "(formerly EdgeDB)" note
- **All path references**: Updated from `/guides/ecosystem/edgedb` to
`/guides/ecosystem/gel`

### CLI Commands
- `edgedb project init` → `gel project init`
- `edgedb` → `gel` (REPL)
- `edgedb migration create` → `gel migration create`
- `edgedb migrate` → `gel migrate`

### npm Packages
- `edgedb` → `gel`
- `@edgedb/generate` → `@gel/generate`

### Installation & Documentation URLs
- Installation link: `docs.geldata.com/learn/installation` (functional)
- Documentation reference: `docs.geldata.com/` (operational)
- Installation scripts: Verified working (`https://www.geldata.com/sh`
and `ps1`)
- Added Homebrew option: `brew install geldata/tap/gel-cli`

### Code Examples
- Updated all imports: `import { createClient } from "gel"`
- Updated codegen commands: `bunx @gel/generate`

## Verified
All commands verified against official Gel documentation at
https://docs.geldata.com/

Fixes #17721

---------

Co-authored-by: Lydia Hallie <lydiajuliettehallie@gmail.com>

docs/snippets/guides.jsx

@@ -123,7 +123,7 @@ export const GuidesList = () => {
         title: "Ecosystem",
         icon: "puzzle",
         items: [
-          { title: "Use EdgeDB with Bun", href: "/guides/ecosystem/edgedb" },
+          { title: "Use Gel with Bun", href: "/guides/ecosystem/gel" },
           { title: "Use Prisma ORM with Bun", href: "/guides/ecosystem/prisma" },
           { title: "Use Prisma Postgres with Bun", href: "/guides/ecosystem/prisma-postgres" },
           { title: "Create a Discord bot", href: "/guides/ecosystem/discordjs" },