Henry rubato tests

[henry-domingo]

Summary

This PR adds a new end-to-end integration test for the booking journey and documents both the test flow and architecture notes.

What changed

1. Added a new integration test covering the auth-gated local booking flow:

• Starts logged out and verifies Login screen is shown.
• Logs in through a test auth repo override.
• Completes booking creation flow.
• Returns Home and verifies the newly created booking is visible.

2. Updated documentation with:

• How to run this new integration test.
• Architecture walkthrough notes (state-to-UI trace, routing/auth gate behavior, data boundaries, and suggested enhancement).
• Answers to Part 2 and 4 questions.

Key choices and why

1. Used local providers for known test behavior.

• Chose local data path to avoid network/server issues - confining to app's logic

2. Overrode only the auth repository in test setup.

• This keeps routing, VMs, and booking flow intact while still controlling login state transitions.
• Cleared shared preferences at test start.
• Ensures a consistent logged-out initial state so the test remains repeatable.

3. Added explicit screen/state assertions at each major step.

• Makes failures easier to notice and provides assurance in flow coverage.

How to run

• Refer to the branch's README

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