chore: Update package manager and ignore requirements-dev.txt

[yihong0618]

Fix issue vercel error: spawn pip3 ENOENT by:

• Update packageManager field from "pnpm@8.7.0" to "yarn@1.22.22"
• Add requirements-dev.txt to .vercelignore

close: #627

@ben-29 can you help to review, maybe workouts_page also need this

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