Document format parameter (json,text) for logs endpoints

## Documentation Check

### Previous Feedback
**Not yet addressed** - The suggestion from the previous doc-check review (2026-01-29) has not been implemented.

### Updates Needed
- [ ] `docs/admin/monitoring/logs.md` - Add section explaining the new `?format=text` query parameter for viewing raw logs
- Document that users can append `?format=text` to log API endpoints to get plain text output with RFC3339 timestamps
- Explain that this format is useful for sharing logs externally, viewing in browser, or using with curl/wget
- Note the limitation: cannot be combined with `follow=true` (streaming)
- List the four endpoints that support this parameter:
- `/api/v2/workspaceagents/{id}/logs?format=text`
- `/api/v2/workspacebuilds/{id}/logs?format=text`
- `/api/v2/templateversions/{id}/logs?format=text`
- `/api/v2/templateversions/{id}/dry-run/{jobID}/logs?format=text`
- Mention that "View raw logs" links are available in the UI (workspace build page, template editor, template version page)
- Include example: `curl https://coder.example.com/api/v2/workspacebuilds/{build-id}/logs?format=text`

### Rationale
The PR is fully implemented with UI links and backend functionality, but user-facing documentation explaining the feature is still missing. Users seeing "View raw logs" links in the UI will want to understand:
- What the raw format provides (RFC3339 timestamps + plain text)
- When to use it (sharing logs, external tools, debugging)
- How to use it programmatically (API endpoints with `?format=text`)
- What limitations exist (no streaming support)

The auto-generated API reference docs document the parameter but don't explain the use case or workflow.

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*Automated review via [Coder Tasks](https://coder.com/docs/ai-coder/tasks)*

_Originally posted by @coder-tasks[bot] in https://github.com/coder/coder/issues/21727#issuecomment-3840116744_