Complete E2E test implementation and CI fixes

[patchmemory]

Summary

This PR completes the E2E testing initiative by implementing all 5 remaining E2E tasks from the Ready Queue:

• ✅ task:e2e:00-contracts-and-taxonomy: Contract tests and test taxonomy documentation
• ✅ task:e2e:01-helpers: Pytest test helpers package with examples
• ✅ task:e2e:03-core-flows: Comprehensive core flow tests (scan → browse → details)
• ✅ task:e2e:04-negatives: Negative path and error handling tests
• ✅ task:e2e:05-ci-docs: CI integration and complete testing documentation

Changes

New Tests

• e2e/core-flows.spec.ts: 3 comprehensive E2E tests covering full user workflows
• tests/test_helpers_example.py: 4 tests demonstrating all test helper modules (rclone, neo4j, builders, asserts)
• All existing E2E tests passing (12 total Playwright tests)

CI Fixes

• .github/workflows/dev-submodule-sync.yml: Fixed GitHub token authentication for dev submodule access
  • Added token: ${{ secrets.GITHUB_TOKEN }} to checkout step
  • Configured git credentials helper for HTTPS submodule cloning
  • Resolves "fatal: could not read Username" error when syncing dev submodule

Documentation

• docs/testing.md: Added 101 lines of comprehensive E2E testing documentation
  • E2E Testing Complete Guide with quickstart instructions
  • CI Integration details and artifact access
  • Troubleshooting section for common E2E and pytest issues

Other Changes

• e2e/global-setup.ts: Use python3 on Linux/Mac for cross-platform compatibility
• tests/e2e/conftest.py: Enhanced pytest-playwright fixtures
• tests/e2e/test_home_scan.py: Removed duplicate test (moved to Playwright)

Test Results

Playwright E2E (12 tests):

✓ smoke.spec.ts: home loads without console errors
✓ browse.spec.ts: files page loads and shows stable hooks  
✓ scan.spec.ts: scan temp directory and verify on Home
✓ core-flows.spec.ts: complete flow scan → browse → file details (3 tests)
✓ negative.spec.ts: error handling, empty states, edge cases (7 tests)

pytest (113 tests, excluding e2e marker):

• All unit tests passing
• All contract tests passing
• All integration tests passing
• Test helpers verified with example tests

CI Verification

This PR will be validated by:

1. python-tests job: pytest suite (113 tests)
2. e2e job: Playwright tests (12 tests)
3. verify-dev-submodule job: dev submodule freshness check

Merge Readiness

• All E2E tasks completed (5/5)
• Tests passing locally
• CI workflows configured and fixed
• Documentation complete with troubleshooting
• Dev submodule clean
• Ready to merge to main

🤖 Generated with Claude Code

Co-Authored-By: Claude noreply@anthropic.com