feat: add Playwright E2E test suite for auth, dashboard, goals, streak, and API routes

[IshitaSingh0822]

Summary

Adds a Playwright E2E test suite to DevTrack covering auth flow, dashboard widget rendering, goals CRUD, streak widget, and critical API routes.
Closes #2120

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Type of Change

• Bug fix
• New feature
• Documentation update
• Refactor / code cleanup

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Changes Made

• Added e2e/auth.spec.ts — landing page load, sign-in button visible, OAuth redirect fires, unauthenticated dashboard redirects
• Added e2e/dashboard.spec.ts — mock login via encode() + addCookies(), all 6 widgets render, no uncaught console errors
• Added e2e/goals.spec.ts — create goal POST fires with correct payload, goal appears in list, delete removes it
• Added e2e/streak.spec.ts — current/longest streak values visible, freeze button present and triggers API call
• Added e2e/api.spec.ts — /api/metrics/contributions returns 200 with valid session, 401 without; goals POST returns 401 without session
• Updated README.md with E2E test suite documentation, spec table, and local run instructions

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How to Test

1. Install Playwright browsers: npx playwright install --with-deps chromium
2. Run the full suite: npm run test:e2e
3. Run a single spec: npx playwright test e2e/goals.spec.ts
4. View HTML report: npx playwright show-report

No real GitHub or Supabase credentials required — all external calls are mocked via page.route().

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Screenshots (if UI change)

N/A

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Checklist

• Linked issue in summary
• npm run lint passes locally
• No TypeScript errors (npm run type-check)
• Self-reviewed the diff
• Added/updated tests if applicable

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Accessibility Checklist

• Proper keyboard navigation tested
• Responsive UI verified
• Accessibility labels added where needed

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Additional Notes

All 5 spec files have at least 3 assertions each. No real tokens needed in CI — mocked via page.route(). Existing specs (landing.spec.js, auth-bypass.spec.js, etc.) are untouched.

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[github-actions]

GSSoC Label Checklist 🏷️

@Priyanshu-byte-coder — please apply the appropriate labels before merging:

Difficulty (pick one):

• level:beginner — 20 pts
• level:intermediate — 35 pts
• level:advanced — 55 pts
• level:critical — 80 pts

Quality (optional):

• quality:clean — ×1.2 multiplier
• quality:exceptional — ×1.5 multiplier

Validation (required to score):

• gssoc:approved — counts for points
• gssoc:invalid / gssoc:spam / gssoc:ai-slop — does not score

Type labels (type:*) are auto-detected from files and title. Review and adjust if needed.
Points formula: (difficulty × quality_multiplier) + type_bonus

[github-actions]

🎉 Merged! Thanks for contributing to DevTrack.

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