feat: upgrade React 16 to 18 and migrate Enzyme tests to RTL

[felixrieseberg]

Summary

Upgrade React from 16.14 to 18.3 as a prerequisite for migrating from Blueprint.js to shadcn/ui.

Changes

Core React 18 migration

• Upgraded react/react-dom from ^16.14.0 to ^18.3.1
• Upgraded react-mosaic-component from ^4.1.1 to ^6.1.1
• Upgraded @testing-library/react from ^12.1.5 to ^16.1.0
• Migrated ReactDOM.render() to createRoot().render() in src/renderer/app.tsx
• Added src/blueprint-react18.d.ts with module augmentations for Blueprint v3 children prop compatibility
• Added @types/react resolution to prevent duplicate type versions

React 18 behavioral fixes

• Fixed handleChannelChange in settings-electron.tsx to derive toggle from state instead of event.currentTarget.checked
• Added null check for this.context?.mosaicActions in output.tsx

Test migration (Enzyme to RTL)

• Removed enzyme, enzyme-adapter-react-16, enzyme-to-json and their @types packages
• Migrated all 21 Enzyme test files to React Testing Library
• Deleted 19 obsolete snapshot files
• Added crypto.subtle polyfill in tests/setup.ts for jsdom compatibility
• Fixed pre-existing RTL tests for React 18 compatibility (act, waitFor, MobX observer re-rendering)

Verification

• tsc --noEmit: 0 errors
• vitest run: 91 files, 805 passed, 0 failed
• eslint: 0 errors
• yarn start: app builds and launches successfully

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	npm/​@​types/​react-dom@​16.9.12 ⏵ 18.3.7			+2
	npm/​@​types/​react@​16.14.6 ⏵ 18.3.27			+2	+3
	npm/​react-mosaic-component@​4.1.1 ⏵ 6.1.1			+1
	npm/​react@​16.14.0 ⏵ 18.3.1	+1		+7
	npm/​react-dom@​16.14.0 ⏵ 18.3.1	+1		+2
	npm/​@​testing-library/​react@​12.1.5 ⏵ 16.3.2

View full report

[coveralls]

coverage: 77.931% (-0.6%) from 78.498%
when pulling 9b35f4d on felixr/react-18
into ee5c030 on main.

[dsanders11]

Could we split off the test migrations into a separate PR? It'll be easier to tell which changes are only in service of the RTL migration, versus which changes are also part of the React 18 upgrade.

[felixrieseberg]

Splitting into two separate PRs: one for React 18 upgrade, one for Enzyme→RTL test migration.