## Description
This PR fixes a `RangeError: Invalid language tag` that occurs in the
Heatmap report when using locales with underscores (e.g., `pt_BR`,
`zh_TW`).
The issue was caused by passing the raw locale string from `vue-i18n`
(which uses underscores for some regions) directly to
`Intl.DateTimeFormat`. The `Intl` API expects BCP 47 language tags which
use hyphens (e.g., `pt-BR`).
This change sanitizes the locale string by replacing underscores with
hyphens before creating the `DateTimeFormat` instance.
Fixes#12951
7e0507e3b5