[Bug]: `metamaskbot` broken beta build links

### Describe the bug

Each `metamaskbot` PR comment includes broken beta build links. We don't currently produce beta builds as part of PR status checks. The links were temporarily removed in #29403 but we still need them shown when a beta build is triggered.

### Expected behavior

Either create beta builds and link them, or conditionally show the links (correctly) only when a beta build was triggered.

### Screenshots/Recordings

_No response_

### Steps to reproduce

Example: https://github.com/MetaMask/metamask-extension/pull/29371#issuecomment-2556292709

### Error messages or log output

```shell

```

### Detection stage

On main branch

### Version

main

### Build type

Other (please specify exactly where you obtained this build in "Additional Context" section)

### Browser

Other (please elaborate in the "Additional Context" section)

### Operating system

Other (please elaborate in the "Additional Context" section)

### Hardware wallet

_No response_

### Additional context

_No response_

### Severity

_No response_

No file or test is named. Start by tracing the metamaskbot PR comment generation and beta-build trigger/status-check path, using PR #29371 and the temporary removal in #29403 as references. Done means beta links appear only when a beta build was triggered, or the links point to valid builds that are produced.

Written by the indexing model from the issue text.