Add `--failed-jobs-only` flag to `glab ci get`
## Summary
Extend the existing `glab ci get` command with two new flags to support filtering jobs by status for a given merge request:
- `--mr=<mr-id>` to target the latest pipeline of a specific merge request
- `--failed-jobs-only` as a convenience alias for `--filter-jobs='select(.status == "failed")'`
## Motivation
When working with merge requests, it is common to need to quickly identify which CI jobs are failing in the latest pipeline. Currently, users need to navigate to the GitLab UI or run multiple commands to get this information. Extending `glab ci get` with these flags would streamline the workflow for developers working from the terminal.
## Proposed Command
```
glab ci get --mr=<mr-id> --failed-jobs-only
```
### Example Usage
```sh
# List failing jobs in the latest pipeline of MR !42
glab ci get --mr=42 --failed-jobs-only
# Equivalent explicit form
glab ci get --mr=42 --filter-jobs='select(.status == "failed")'
```
### Flag Details
| Flag | Description |
|------|-------------|
| `--mr=<mr-id>` | Target the latest pipeline of the given merge request |
| `--failed-jobs-only` | Alias for `--filter-jobs='select(.status == "failed")'` |
| `--filter-jobs=<expr>` | Filter jobs using a jq-style expression |
### Expected Output
The command should output a list of failing jobs, including relevant details such as:
- Job name
- Job ID
- Stage
- Failure reason / status
- Link to the job log
## Acceptance Criteria
- [ ] `--mr=<mr-id>` flag is added to `glab ci get` to resolve the latest pipeline for the given MR
- [ ] `--failed-jobs-only` flag is added as an alias for `--filter-jobs='select(.status == "failed")'`
- [ ] `--filter-jobs` flag supports jq-style expressions for flexible job filtering
- [ ] Output includes job name, ID, stage, and a link to the job
- [ ] Command supports the `--output` / `-F` flag for different output formats (e.g., JSON)
- [ ] Help text and documentation are updated for the new flags
- [ ] Unit and integration tests are added
issue