feat: implement Playwright E2E test suite and CI automation (#372)

[Sam-Rytech]

Description

This PR introduces a robust End-to-End (E2E) testing framework using Playwright to ensure the stability of the FlowFi stream lifecycle. It automates the verification of core features from the user's perspective, including wallet integration and real-time stream management.

Changes

• Testing Suite: Created frontend/e2e/stream-lifecycle.spec.ts to test:
  • Mocked Freighter wallet connection.
  • Stream creation wizard flow.
  • Dashboard visibility and real-time updates.
  • Stream controls (Pause, Resume, Cancel).
• CI/CD Pipeline: Updated .github/workflows/ci.yml to include:
  • A new e2e-tests job that runs after the frontend build.
  • Automated browser binary caching to reduce runtimes.
  • HTML report generation and artifact uploading on test failure for debugging.

Verification Results

• All 6 scenarios pass in headless Chromium.
• CI job successfully triggers on push.
• Playwright report is accessible via GitHub Actions artifacts.

Closes #372

[ogazboiz]

hey, main was failing CI from broken auth imports + frontend parse errors. fixed and pushed to main now. please rebase to pick up the fixes:

git fetch upstream
git rebase upstream/main
git push --force-with-lease

if there's a conflict, resolve it locally and we'll review once CI is green.

[Sam-Rytech]

@ogazboiz These fails have nothing to do with files I worked on

[ogazboiz]

hey, main CI is fully green now. there were several real TypeScript and test issues from #444's merge that have all been fixed. please rebase one more time:

git fetch upstream
git rebase upstream/main
git push --force-with-lease

your PR's diff should be much cleaner after this rebase since main now has the canonical versions of cancel.ts, sorobanService.ts, and the withdraw test.