[App] Add `.github/` workflows for the frontend

[Lex-Studios]

Description:
The frontend has no CI/CD configuration.

Tasks:

• Create .github/workflows/lint.yml that runs pnpm lint on every PR.
• Create .github/workflows/build.yml that runs pnpm build on every PR to catch build errors.
• Add a pnpm type-check script and include it in CI.

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[SamixYasuke]

@SamixYasuke has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

Hi maintainer, I'd like to handle this issue, thanks

ℹ️ Repo Maintainers: To accept this application, review their application or assign @SamixYasuke to this issue.

[SudiptaPaul-31]

@SudiptaPaul-31 has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

May I be assigned to this issue I have worked on several open-source projects and also an active open-source contributor and would love to contribute to this issue. I have worked with more than 30+ open-source projects and delivered quality pr's for them which led to faster project delivery

ℹ️ Repo Maintainers: To accept this application, review their application or assign @SudiptaPaul-31 to this issue.