fix: remove CardGroup/Columns wrapping external Card links to fix double-tab bug

[lin-bot23]

Problem

Clicking a Card with an external href inside CardGroup or Columns opens two browser tabs instead of one. This is a Mintlify framework-level bug in how these wrapper components handle event propagation for external links.

Root Cause

Mintlify's CardGroup and Columns components trigger duplicate navigation events for Cards with external href values. Internal links (relative paths like /tutorials/...) are not affected.

Fix

All external-link Cards previously wrapped in CardGroup or Columns are now rendered as standalone Cards (vertically stacked). Internal-link Cards inside groups are preserved.

Scope

• 137 files modified across all three locales (EN, ZH, JA)
• Exceptions: lens.mdx files - the CardGroup containing external links is entirely comment-blocked (/* ... */), so it was left untouched.

Testing

Verified on local Mintlify dev preview:

• Standalone Cards -> single tab (OK)
• Columns-wrapped external Cards -> double tab (framework bug confirmed)
• Internal-link Cards in groups -> single tab (OK, unchanged)