omarchy-nvim ships a dead plugin URL: `gthelding/monokai-pro.nvim` 404s, so `:Lazy sync` reports "fetch failed"

## What happens

On a stock install, opening Neovim and running `:Lazy sync` (or `:Lazy check` / `:Lazy update`) reports:

```
Failed (1)
  monokai-pro.nvim   fetch failed
    fatal: could not read Username for 'https://github.com': terminal prompts disabled
```

The plugin is already present at the pinned commit from the packaged cache, so themes still work, but every sync/update flags it as failed and the error is alarming.

## Cause

`~/.config/nvim/lua/plugins/all-themes.lua` (owned by `omarchy-nvim`) declares:

```lua
{
    "gthelding/monokai-pro.nvim",
    lazy = true,
    priority = 1000,
},
```

`https://github.com/gthelding/monokai-pro.nvim` now returns **HTTP 404** — the fork has been deleted (or made private). The git endpoint returns 401, which is why git falls back to prompting for a username and lazy.nvim reports "could not read Username / terminal prompts disabled".

`lazy-lock.json` pins `monokai-pro.nvim` to `5b06ae0736813b1c65d76a4be9edbe92be0b9c74` on that fork.

## Expected

`:Lazy sync` completes with no failures on a stock config.

## Steps to reproduce

1. Fresh Omarchy 4 install (omarchy-nvim 2026.8.13-1).
2. `nvim`
3. `:Lazy sync`
4. Observe `monokai-pro.nvim` under **Failed** with the git username error.

## Suggested fix

Point the spec at the canonical, actively maintained upstream that the dead repo was forked from — `loctvl842/monokai-pro.nvim` (HTTP 200, still the source of the `ristretto` filter Omarchy's Monokai theme uses):

```lua
{
    "loctvl842/monokai-pro.nvim",
    lazy = true,
    priority = 1000,
},
```

and refresh the `lazy-lock.json` pin. (`gthelding/monokai-pro.nvim` was a thin fork of it.)

## System

- Omarchy: 4.0.2-1
- omarchy-nvim: 2026.8.13-1
- Neovim: v0.12.5
- Arch, kernel 7.1.9-arch1-2