[Vis skill] Fixes ES|QL escaping drift during visualization config generation (elastic#272493)

## Summary

Fixes ES|QL escaping drift during visualization config generation. 

## What Was Not Working
`generate_esql` produced the correct query for a GROK pattern:

```esql
| GROK message "%{IP} - - \\[%{DATA}\\] \"%{WORD:method} %{DATA}\""
```

But when the visualization config was generated, the query embedded in
`visualization.data_source.query` lost one escaping level for the
bracket regex:

```esql
| GROK message "%{IP} - - \[%{DATA}\] \"%{WORD:method} %{DATA}\""
```

That happened because the prompt asked the model to manually place raw
ES|QL inside a JSON string. For ES|QL containing backslashes and quotes,
JSON serialization needs an additional escaping layer. The
model-generated visualization looked correct visually, but after JSON
parsing it no longer matched the authoritative ES|QL.

## Description
This change ensures visualization configs preserve the ES|QL query
produced by the graph. The prompt now embeds the ES|QL query as a
JSON-encoded string, preventing raw interpolation from dropping escape
levels for patterns like `GROK`.
Before:
<img width="639" height="854" alt="Screenshot 2026-06-03 at 14 25 37"
src="https://github.com/user-attachments/assets/bd339e4a-57e6-4b5a-a1fd-6e7f606027a6"
/>

After:
<img width="666" height="687" alt="Screenshot 2026-06-03 at 14 25 31"
src="https://github.com/user-attachments/assets/c06d7dd0-862c-464a-9433-841422c9fbab"
/>


## Test Plan
- `node scripts/jest
x-pack/platform/packages/shared/agent-builder/agent-builder-tools-base/visualization/graph_lens.test.ts`
- `node scripts/eslint
x-pack/platform/packages/shared/agent-builder/agent-builder-tools-base/visualization/graph_lens.ts
x-pack/platform/packages/shared/agent-builder/agent-builder-tools-base/visualization/graph_lens.test.ts
x-pack/platform/packages/shared/agent-builder/agent-builder-tools-base/visualization/prompts.ts`


### Checklist

Check the PR satisfies following conditions. 

Reviewers should verify this PR satisfies this list as well.

- [ ] Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/src/platform/packages/shared/kbn-i18n/README.md)
- [ ]
[Documentation](https://www.elastic.co/guide/en/kibana/master/development-documentation.html)
was added for features that require explanation or tutorials
- [ ] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [ ] If a plugin configuration key changed, check if it needs to be
allowlisted in the cloud and added to the [docker
list](https://github.com/elastic/kibana/blob/main/src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker)
- [ ] This was checked for breaking HTTP API changes, and any breaking
changes have been approved by the breaking-change committee. The
`release_note:breaking` label should be applied in these situations.
- [ ] [Flaky Test
Runner](https://ci-stats.kibana.dev/trigger_flaky_test_runner/1) was
used on any tests changed
- [ ] The PR description includes the appropriate Release Notes section,
and the correct `release_note:*` label is applied per the
[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)
- [ ] Review the [backport
guidelines](https://docs.google.com/document/d/1VyN5k91e5OVumlc0Gb9RPa3h1ewuPE705nRtioPiTvY/edit?usp=sharing)
and apply applicable `backport:*` labels.

### Identify risks

Does this PR introduce any risks? For example, consider risks like hard
to test bugs, performance regression, potential of data loss.

Describe the risk, its severity, and mitigation for each identified
risk. Invite stakeholders and evaluate how to proceed before merging.

- [ ] [See some risk
examples](https://github.com/elastic/kibana/blob/main/RISK_MATRIX.mdx)
- [ ] ...

Author: mbondyra

x-pack/platform/packages/shared/agent-builder/agent-builder-tools-base/visualization/prompts.ts

@@ -29,6 +29,7 @@ export const createGenerateConfigPrompt = ({
 }): BaseMessageLike[] => {
   const chartTypeConfigPromptContent = getChartTypeConfigPromptContent(chartType);
   const colorPalettesPromptContent = getColorPalettesPromptContent(chartType);
+  const esqlQueryJson = JSON.stringify(esqlQuery);
 
   return [
     [
@@ -51,7 +52,7 @@ ${
 }
 
 DATASET RULES:
-1. The 'dataset' field must contain: { type: "esql", query: "${esqlQuery}" }
+1. The 'dataset' field must contain: { type: "esql", query: ${esqlQueryJson} }
 2. For ES|QL column bindings use { column: '<esql column name>', ...other options }
 3. All field names must match those available in the ES|QL query result
 4. Follow the schema definition strictly