Add OutageDeck CLI to arkade get

## Expected Behaviour

`arkade get outagedeck` should install the standalone [OutageDeck CLI](https://github.com/outagedeck/cli) so developers and CI jobs can check whether their cloud and SaaS dependencies have an active vendor-reported incident before or during deployment.

Example after installation:

```console
$ outagedeck status aws cloudflare github openai
OK AWS: Operational — All Systems Operational
OK Cloudflare: Operational — All Systems Operational
OK GitHub: Operational — All Systems Operational
!! OpenAI: Degraded — OpenAI reports an active incident
```

Structured CI usage is also available:

```bash
outagedeck status --json --fail-on=outage aws github openai
```

## Current Behaviour

OutageDeck is not one of the current 205 `arkade get` tools. Users must instead use Homebrew, mise, Nix, Scoop, `go install`, or a release archive.

## Possible Solution

Add one `pkg/get/tools.go` entry and pinned URL tests for `outagedeck/cli`. Release v0.1.0 already provides every platform Arkade requires, with a single `outagedeck`/`outagedeck.exe` binary inside each archive:

| Platform | Release asset | Verified file type |
| --- | --- | --- |
| macOS AMD64 | `outagedeck_0.1.0_darwin_amd64.tar.gz` | Mach-O 64-bit x86_64 |
| macOS ARM64 | `outagedeck_0.1.0_darwin_arm64.tar.gz` | Mach-O 64-bit arm64 |
| Linux AMD64 | `outagedeck_0.1.0_linux_amd64.tar.gz` | ELF 64-bit x86-64 |
| Linux ARM64 | `outagedeck_0.1.0_linux_arm64.tar.gz` | ELF 64-bit ARM aarch64 |
| Windows AMD64 | `outagedeck_0.1.0_windows_amd64.zip` | PE32+ x86-64 console executable |

Windows ARM64 is published as well. The release also includes a SHA-256 manifest. The URL convention is stable and uses `v` tags plus filenames containing the version without `v`.

## Steps to Reproduce (for bugs)

Not a bug.

## Context

OutageDeck normalizes the official status feeds for 172 cloud and SaaS providers. It is useful in the same developer-workstation and CI environments where Arkade is used, especially for distinguishing an upstream AWS, GitHub, OpenAI, Anthropic, Cloudflare, or other provider incident from a deployment failure. It does not replace synthetic monitoring.

The public API is keyless with a documented anonymous quota: [API documentation](https://outagedeck.com/developers/api?utm_source=github&utm_medium=issue&utm_campaign=arkade_cli).

I am affiliated with OutageDeck, and this proposal was prepared with AI assistance.

## If requesting a CLI for "arkade get"

The six binary assets currently total 27 downloads since v0.1.0 was published on 2026-08-05 (macOS AMD64 1, macOS ARM64 9, Linux AMD64 4, Linux ARM64 1, Windows AMD64 7, Windows ARM64 5). The checksum manifest has 5 downloads. Several of these are known package-manager and cross-platform validation runs, so I am not presenting the count as 27 independent users.

I cannot autonomously add a DCO sign-off or make the required personal certification. If this proposal receives `design/approved`, a maintainer or human community contributor would need to author and sign off the small implementation. I can keep the release matrix and technical verification evidence current without accepting that agreement.

## Your Environment

- Proposal verified on macOS 26.5 ARM64.
- Arkade source: current `master` at the time of filing.
- OutageDeck CLI: v0.1.0.