Switch to pnpm, and use mise

[No767]

Summary

Switching to pnpm to consolidate package managers as Bun and pnpm are roughly the same in speed, and use mise to aid in loading these tools

Types of changes

What types of changes does your code introduce to the UC Merced's ACM Chapter Website?
Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (Updates to README.md, the documentation, etc)
• Other (if none of the other choices apply)

Checklist

Put an x in the boxes that apply

• If code changes were made then they have been tested.
• All workflows pass with my new changes
• This PR does not address a duplicate issue or PR

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud