ci: add GitHub Actions workflows for owner-portal CI and PR validation

[PranavGadge01]

Summary

Adds GitHub Actions CI/CD workflows for the owner-portal and general PR validation.

Workflows Added

owner-portal-ci.yml

Triggers on push or pull request to main when files inside owner-portal/ change.

• Sets up Node.js 18 with npm caching
• Installs dependencies with --legacy-peer-deps
• Runs production build via npm run build
• Uploads build artifacts for 7 days

pr-checks.yml

Triggers on every pull request to main.

• Scans for accidentally committed .env files
• Scans for hardcoded secrets in source files
• Fails the PR if either check is violated

Why

• Catches build failures before they reach main
• Prevents accidental secret exposure (relevant after issue fix: owner-portal fails to start due to deprecated createPrivyWagmiConfig and duplicate imports #31)
• Keeps the owner-portal always in a deployable state
• Directly supports the GSoC goal of CI/CD automation for LensMint

Testing

• Workflow syntax validated
• Paths filter ensures workflow only runs when owner-portal files change
• Secret detection covers .js, .jsx, .ts, .tsx files