[33] Add GitHub Actions CI for StepFi-App

[EmeditWeb]

Problem

The mobile app repo has no CI workflow. A typo in any component can break the Expo build and only be discovered when EAS build fails hours later.

Context

Expo builds are slow and rate-limited. Catching compile errors at PR time via a cheap expo export --platform web is dramatically faster than waiting for an EAS run.

Before Starting

Read these context files first:

• context/architecture-context.md
• context/code-standards.md
• context/progress-tracker.md

What To Build

1. Create .github/workflows/ci.yml in StepFi-App.
2. Triggers: pull_request and push to main.
3. Job web-build: ubuntu-latest, Node 20, cache npm.
4. Steps: checkout → setup-node → npm ci → npx expo export --platform web.
5. Upload web build as artifact for inspection.
6. Status badge in README.

Files To Touch

• .github/workflows/ci.yml
• README.md

Acceptance Criteria

• Workflow runs on every PR to main
• Failed Expo export blocks merge
• node_modules cached
• Web bundle uploaded as artifact
• Status badge in README
• Run time under 7 minutes

Mandatory Checks Before PR

• CI passes on a test PR before merging
• Zero secrets committed to the repo
• context/progress-tracker.md updated

[deslawson]

I can work onthis issues ,assign please