docs: update Log Searching Agent docs and catalog

> [!CAUTION]
> Protected files were modified in this change.
> This pull request is in `request_review` mode and requires explicit human scrutiny before merge.
>
> Protected files: `README.md`

## Summary
- Update `gh-agent-workflows/log-searching-agent/README.md` to correctly state that `create-issue` does **not** auto-close older reports.
- Add Log Searching Agent to the event-driven workflows catalog table in `docs/workflows/gh-agent-workflows.md`.
- Add the missing docs page at `docs/workflows/gh-agent-workflows/log-searching-agent.md` and include it in `mkdocs.yml` nav so catalog/link validation remains consistent.

## Validation
- `python3 scripts/check-nav-catalog.py`

## Issue
Closes \#2048

---
[What is this?](https://ela.st/github-ai-tools) | [From workflow: Trigger Docs Patrol](https://github.com/elastic/ai-github-actions/actions/runs/34362509928)

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---

> [!NOTE]
> This was originally intended as a pull request, but the git push operation failed.
>
> **Original error:** ERR_VALIDATION: pushSignedCommits: refusing unsigned push for branch 'fix-issue-2048-log-searching-agent-docs-e0163988cb9c96e3': Signed-commit payload violates file-protection policy (request_review): gh-agent-workflows/log-searching-agent/README.md
>
> **Workflow Run:** [View run details and download bundle artifact](https://github.com/elastic/ai-github-actions/actions/runs/34362509928)
>
> The bundle file is available in the `agent` artifact in the workflow run linked above.

To create a pull request with the changes:

```sh
# Download the artifact from the workflow run
gh run download 34362509928 -n agent -D /tmp/agent-34362509928

# Fetch the bundle into a temporary ref, then update the local branch
git fetch /tmp/agent-34362509928/aw-fix-issue-2048-log-searching-agent-docs.bundle refs/heads/fix-issue-2048-log-searching-agent-docs:refs/bundles/create-pr-fix-issue-2048-log-searching-agent-docs-e0163988cb9c96e3-1625c5e4
git update-ref refs/heads/fix-issue-2048-log-searching-agent-docs-e0163988cb9c96e3 refs/bundles/create-pr-fix-issue-2048-log-searching-agent-docs-e0163988cb9c96e3-1625c5e4
git checkout fix-issue-2048-log-searching-agent-docs-e0163988cb9c96e3
# Ensure the working tree matches the updated branch
git reset --hard
# Remove the temporary bundle ref
git update-ref -d refs/bundles/create-pr-fix-issue-2048-log-searching-agent-docs-e0163988cb9c96e3-1625c5e4

# Push the branch to origin
git push origin fix-issue-2048-log-searching-agent-docs-e0163988cb9c96e3

# Create the pull request
gh pr create --title 'docs: update Log Searching Agent docs and catalog' --base main --head fix-issue-2048-log-searching-agent-docs-e0163988cb9c96e3 --repo elastic/ai-github-actions
```

Start with gh-agent-workflows/log-searching-agent/README.md, docs/workflows/gh-agent-workflows.md, docs/workflows/gh-agent-workflows/log-searching-agent.md, and mkdocs.yml. Run python3 scripts/check-nav-catalog.py; done means the README wording, catalog entry, docs page, and navigation are consistent and validation passes.

Written by the indexing model from the issue text.