Function articleHasChart

Detect whether the article contains at least one Chart.js canvas with a well-formed data-chart-config JSON payload.

A valid chart must:

• be rendered via <canvas data-chart-config="…"> (the declarative CSP-safe pattern hydrated by js/chart-init.js)
• declare a supported Chart.js type
• carry at least 3 data points in the first dataset (single-point charts are rejected by SHARED_PROMPT_PATTERNS.md anti-patterns)