Add support for official GitHub warning markup

[daun]

Description

• Support GitHub's official markdown warning format
• Ensure identical rendering in readmes vs. the official docs
• The old format is actually no longer supported, but I thought no harm in leaving it in
• We only have green and red, so I made warning and caution red, everything else green
• There's no lightbulb icon in feather, but the zap icon felt close enough conceptionally

New format (now supported)

> [!NOTE]  
> Highlights information that users should take into account, even when skimming.

> [!TIP]
> Optional information to help a user be more successful.

> [!IMPORTANT]  
> Crucial information necessary for users to succeed.

> [!WARNING]  
> Critical content demanding immediate user attention due to potential risks.

> [!CAUTION]
> Negative potential consequences of an action.

Old format (still supported)

> **Note**
> This is a note

> **Warning**
> This is a warning

Screenshot

Checks

• [ ] The PR is submitted to the master branch
• [ ] The code was linted before pushing (npm run lint)
• [ ] All tests are passing (npm run test)
• [ ] New or updated tests are included
• [ ] The documentation was updated as required

Additional information

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[daun]

🏎️