* fix(ent3): Add link target and experimental caution for PachaTree option.
* feat(ent3): add experimental badge for --use-pacha-tree
Document the experimental PachaTree storage engine option with a
styled badge and caution callout. Add reusable .badge.experimental
class using the existing caution color palette for light/dark modes.
- Add experimental badge to serve options table and config-options
- Add badge theme variables referencing $article-caution-* colors
- Use custom heading ID to preserve #use-pacha-tree anchor
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