Added support for TypeScript

[david-yz-liu]

Proposed Changes

(Describe your changes here. Also describe the motivation for your changes: what problem do they solve, or how do they improve the application or codebase? If this pull request fixes an open issue, use a keyword to link this pull request to the issue.)

Adopted TypeScript v7 into the existing webpack/Babel/Jest toolchain. To minimize changes, the checkJs typescript config is set to false, so existing .js/.jsx files are unchecked. As a proof of concept, the Button component is modified to .tsx, allowing it to be checked with typescript.

Because TypeScript 7.0 ships only a native CLI binary with no stable programmatic API yet (expected in 7.1), ts-loader/fork-ts-checker-webpack-plugin/typescript-eslint's parser aren't usable right now. Babel handles syntax for webpack/Jest, and standalone tsc handles type-checking.

Adds new command pnpm run typecheck to run TypeScript type-checking (tsc); this command is integrated into the CI.

Also extended ESLint configuration to check .ts and .tsx files. Note: the changes revealed that .jsx files currently aren't being linted by ESLint. This should be addressed when migrating files over to typescript.

Screenshots of your changes (if applicable)

Type of Change

(Write an X or a brief description next to the type or types that best describe your changes.)

Type	Applies?
🚨 Breaking change (fix or feature that would cause existing functionality to change)
✨ New feature (non-breaking change that adds functionality)
🐛 Bug fix (non-breaking change that fixes an issue)
🎨 User interface change (change to user interface; provide screenshots)
♻️ Refactoring (internal change to codebase, without changing functionality)	X
🚦 Test update (change that only adds or modifies tests)
📦 Dependency update (change that updates a dependency)	X
🔧 Internal (change that only affects developers or continuous integration)

Checklist

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Before opening your pull request:

• I have performed a self-review of my changes.
  • Check that all changed files included in this pull request are intentional changes.
  • Check that all changes are relevant to the purpose of this pull request, as described above.
• I have added tests for my changes, if applicable.
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Questions and Comments

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[coveralls]

Coverage Report for CI Build 35122159342

Coverage decreased (-0.007%) to 59.82%

Details

• Coverage decreased (-0.007%) from the base build.
• Patch coverage: 1 of 1 lines across 1 file are fully covered (100%).
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	4340
Covered Lines:	2646
Line Coverage:	60.97%
Relevant Branches:	991
Covered Branches:	543
Branch Coverage:	54.79%
Branches in Coverage %:	Yes
Coverage Strength:	153.87 hits per line

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💛 - Coveralls