test(e2e): add full player journey e2e test

[AbdulSnk]

Summary

Adds an end-to-end test for the complete player journey, per #625.
The application had solid coverage on individual modules, but no
single test verified that a player can actually go from start to
finish in a real game session.

What's covered

• Player registration / login
• Starting a new game
• Making a move
• Reaching a completed (win/loss) game state

Changes

• Added test/player-journey.e2e-spec.ts
• Test follows the existing Jest + Supertest e2e pattern used in
  test/app.e2e-spec.ts, with app.close() added in afterEach
  to avoid leaking open connections between test runs

How to test

npm run test:e2e

Notes for reviewers

This is a sequential test (single it() block) rather than
separate cases per step, since later steps depend on state
(authToken, gameId) created in earlier steps — this keeps the
test representing one continuous journey rather than isolated,
order-dependent test cases.

Closes #625

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