Ci/frontend lint before typecheck

[EmmyKay0026]

What does this PR do?

Adds pnpm lint as a required step in the frontend CI job so lint errors block merges. The job continues to run the existing typecheck, Vitest tests, additional frontend tests, and production build.

Closes #215

Type of change

• Bug fix
• New feature / credential type
• Refactor / cleanup
• Docs
• CI / tooling

Merge requirements

• CI is green — cargo test (contracts), pnpm tsc --noEmit (frontend), pnpm build (frontend), circuit tests — all green
• Greptile confidence ≥ 4/5 — all review comments addressed, no unresolved threads
• Circuit changes: fixtures/<type>/ artifacts updated — N/A, no circuit changes
• No NEXT_PUBLIC_ prefix on server-only env vars — N/A, no environment variable changes
• No identity fields stored or logged after KYC provider call — N/A, no KYC changes
• prehash:false preserved on any issuer signing path touched — N/A, no signing-path changes
• Issuer private key never referenced from client-bundled code — N/A, no client or key-handling changes

✅ Merge requirements

• All CI checks pass (contracts / frontend / circuits as applicable)
• Every Greptile review comment is addressed — no unresolved review threads
• Greptile confidence score is 4/5 or higher

Notes for reviewers

This is a CI-only change. The frontend job now runs pnpm lint before typechecking. The existing pnpm test, additional theme and issuer tests, and pnpm build steps remain required and fail the job normally if unsuccessful.