[Feature] Implement End-to-End Test Suite with Playwright for Critical User Flows

[knoxiboy]

Description
The e2e/ directory exists but may lack comprehensive test coverage. Add Playwright E2E tests for the 5 most critical user flows: login, create task, move task on Kanban, assign task, and filter tasks.

Motivation
E2E tests catch regressions that unit tests miss, especially in full-stack applications where Supabase interactions, auth flows, and UI state must work together correctly.

Implementation

1. Add/update test files in e2e/ with Playwright test cases.
2. Create a e2e/fixtures/ directory with seeded test data for repeatable tests.
3. Configure Playwright to run against a local dev server with a test Supabase instance.
4. Add a GitHub Actions workflow that runs E2E tests on every PR.
5. Add screenshot comparison for visual regression detection on key pages.

Level: Critical | Affected Files: e2e/, .github/workflows/

[knoxiboy]

/assign gssoc'26
@Priyanshu-byte-coder Please assigne this issue to me.

[toshigoel10]

/assign

[github-actions]

@toshigoel10 This issue is already taken by @knoxiboy. Check other open issues!