Implement get_job_log MCP Tool and service
## Proposal
Add support for new MCP tool: `get_job_log` which maps to [`Get a log (trace) of a specific job`](https://docs.gitlab.com/ee/api/jobs.html#get-a-log-trace-of-a-specific-job)
* Add a new API mapping following our framework/annotation approach
* Allow the following arguments from the API documentation
* `id` (required) - The ID or URL-encoded path of the project
* `job_id` (required) - The ID of a job
```ruby
route_setting :mcp, tool_name: :get_job_log, params: [:id, :job_id]
```
### Use case
The MCP server currently supports `get_pipeline_jobs` to list jobs and their status, but there is no way to read the actual log output of a job. AI-assisted CI/CD debugging workflows need to read failing job logs to diagnose compilation errors, test failures, and lint issues. Without this tool, users must fall back to raw API calls (`/projects/:id/jobs/:job_id/trace`).
This is referenced in the planning roadmap (#562157) and governance issue (#567747, listed as `get_job_logs` with `pipeline:logs` scope) but has no standalone implementation issue.
**Note:** The job trace endpoint returns plain text and can be large. Consider supporting optional `line_count` or byte-range parameters to allow truncated retrieval, or truncate server-side to a reasonable limit.
**Parent Epic:** https://gitlab.com/groups/gitlab-org/-/epics/20529
issue