Tabbed content blocks for multi-language examples

[engineervix]

Summary

Support tabbed content blocks — a common pattern in documentation for showing the same example in multiple languages or package managers side by side.

Proposed syntax

::: tabs
@tab Go
\`\`\`go
import "github.com/example/lib"
\`\`\`

@tab Python
\`\`\`python
import example_lib
\`\`\`
:::

Implementation notes

• Implement as an extension to the existing admonition block parser in internal/parser/admonitions.go, or as a separate goldmark extension
• Renders to HTML with <div class="tabs"> + <button role="tab"> + <div role="tabpanel"> structure
• Tab switching handled in assets/main.js — no extra dependency
• Tab state should be remembered in localStorage keyed by tab label (so switching "Go/Python" persists across pages)
• Consider: should all tab groups with the same labels sync? (e.g. switching to "Python" in one block switches all "Python" tabs on the page)