fix(react): add output: 'export' to next.config.js for GitHub Pages build

[Copilot]

next build does not generate an out directory unless output: 'export' is explicitly set — the deploy pipeline was calling npm run export (which requires out/) immediately after next build, causing the job to fail every time.

Change

Added output: 'export' to the isProd && isGitHubPages config block in next.config.js:

...(isProd && isGitHubPages && {
  output: 'export',  // causes next build to emit the out/ directory
  basePath: '/Reminders',
  assetPrefix: '/Reminders/',
  images: { unoptimized: true }
}),

This setting is scoped to the GitHub Pages production build only, leaving Docker and local dev builds unaffected.

Original prompt

Pull request: #252

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