feat: allow highlighting text

`**Heavily invest** into cloning new specimens, to **boost population** growth to unprecedented levels.`
-> **Heavily invest** into cloning new specimens, to **boost population** growth to unprecedented levels.

No files, tests, or entry points are named. Start by locating the TypeScript module that renders game/dialog text and handles markdown-like formatting, then inspect any escaping/sanitization logic that turns `**...**` into literal backtick-style text. Update that path to preserve bold markers, and verify by running the project checks or a local game run that the sample sentence renders as highlighted text.

索引モデルが issue の本文から書いたものです。