Chart: add show_legend toggle, document it, and add e2e test

[lovasoa]

Motivation

• Allow authors to disable the chart legend from SQL using a top-level boolean like false AS show_legend so charts can be rendered without the series legend when desired.
• Keep frontend default behavior unchanged (legend shown) while allowing explicit control from the SQL payload.
• Update the official-site documentation/examples so the new parameter is discoverable and used in an existing example.

Description

• Added a new top-level property to the chart template payload by emitting "show_legend": {{stringify show_legend}} in sqlpage/templates/chart.handlebars so SQL values are passed to the client.
• Wired the payload into ApexCharts options in sqlpage/apexcharts.js with legend: { show: data.show_legend !== false } so the legend is visible by default and hidden only when explicitly false.
• Documented the parameter in examples/official-site/sqlpage/migrations/01_documentation.sql and updated the existing Expenses example to include "show_legend": false.
• Added an end-to-end Playwright test in tests/end-to-end/official-site.spec.ts that loads the documentation page and asserts the Expenses chart renders while its legend is hidden.

Testing

• Ran npm run format which completed successfully and formatted files.
• Installed Playwright browsers with npx playwright install chromium and installed required host libs via apt-get to run headless tests successfully.
• Ran the app under cargo run to serve examples/official-site and executed the Playwright e2e test chart supports hiding legend; the test passed.
• Also ran cargo run -- --help during the workflow to verify the binary built and started as expected.

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[chatgpt-codex-connector]

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