feat: allow variable in chains text

`Your species $$species_name is awesome`
-> `Your species Franc-comtois is awesome`

allowed variables:
- species name
- planet name

The issue only mentions chain text behavior and variable placeholders. Start by locating where chain text is created and rendered, then find any existing placeholder/interpolation logic and check if `$$species_name` and `$$planet_name` are currently supported. Run the relevant text/output tests or game flow tests (if available) and validate the sample string now resolves to concrete species/planet values.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.