Add GitHub CI workflow with mise-action for automated testing

[Copilot]

Implements CI workflow to ensure tests pass on push and PR events using mise for toolchain management.

Changes

• .github/workflows/ci.yml: New workflow using jdx/mise-action@v3
  • Installs mise and configures toolchain (Node 24, Elm 0.19.1, Python 3.14)
  • Executes mise run test task
  • Triggers on push/PR to main/master branches
  • Sets explicit contents: read permission per security best practices

The workflow leverages the existing .mise.toml configuration, requiring no additional setup or dependencies.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Github CI workflow</issue_title>
<issue_description>Setup a Github ci workflow that uses the jdx/mise-action@v3 to ensure mise installed and runs the mise test task. This workflow exists to ensure our tests pass during ci.

We should apply our changes to the repository-devops-fixes branch</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Github CI workflow #39

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