test(e2e): implement Playwright testing infrastructure and inventory workflow (#84)

[krishna28004]

Description

This PR implements Playwright end-to-end testing infrastructure for FlipTrack as part of Issue #84.

Changes made

• Added Playwright configuration and E2E test setup.
• Added global authentication setup for Playwright tests.
• Implemented an end-to-end test for the inventory creation workflow.
• Improved the smoke test by replacing a generic selector with a stable semantic selector.
• Enhanced the demo user creation script to support the Supabase Admin API for reliable test user provisioning.
• Fixed an application bug in AddItemModal where previous form steps were unmounted, causing multi-step form data to be lost during native form submission. The inactive steps are now visually hidden instead, preserving form state.

Verification

• ✅ npm run build
• ✅ npm run typecheck
• ✅ npm run test:e2e

This implementation was verified locally and all Playwright tests pass successfully.

Related Issues

Closes #84

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

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[github-actions]

Codesense Ai: This PR is too large to review automatically. A human maintainer will take a look!

[github-actions]

Codesense Ai: This PR is too large to review automatically. A human maintainer will take a look!

[github-actions]

Codesense Ai: This PR is too large to review automatically. A human maintainer will take a look!