docs: add developer conventions documentation

[Sushma-1706]

Description

What is this PR

• Bug fix
• Addition of a new feature
• Other

Why is this PR needed?

The datashuttle codebase follows several soft developer conventions that have
been mentioned across issues and reviews but were not documented in one place.
This made it harder for new contributors to understand testing expectations and
code structure conventions.

What does this PR do?

This PR adds an initial developer documentation page that records existing
developer conventions, including:

• TUI testing requirements
• Behavior of cloud connection tests (SSH, Google Drive, AWS)
• Backward compatibility testing expectations
• Code organization conventions

The documentation is intentionally lightweight and marked as work in progress.

References

• Closes Developer documentation #533

How has this PR been tested?

This PR adds documentation only and does not modify code or tests.

Is this a breaking change?

No. This PR does not change any runtime behavior or APIs.

Does this PR require an update to the documentation?

Yes. This PR adds developer-facing documentation.

Checklist:

• The documentation has been updated to reflect the changes

[JoeZiminski]

Thanks for this @Sushma-1706, I think it is a nice template to get started with. I think we can remove any references to this being a work in progress, or upcoming additions, because readers will not be that interested. They will mainly use this as a reference guide for working with particularly fiddly parts of the codebase, or for general conventions. As such, some parts will have to be more detailed rather than high level e.g. the backward compatibility tests. Coincidentally, #661 was recently raised highlighting how more information on tests should be included in the contributing guide. I think some of this could be moved there (e.g. cloud connection tests, backwards compatibility tests). Then maybe this developer guide can be put on ice as it won't contain very much. What do you think?

[Sushma-1706]

Thanks for the feedback, that makes sense!

I agree that the “work in progress / future additions” wording can be removed — I’ll clean that up so the page reads more like a stable reference.

For the testing-related sections (cloud connections + backward compatibility), I agree they probably fit better in the contributing guide. I’m happy to move those sections into CONTRIBUTING.md and keep the developer docs focused on code structure and conventions.

If that sounds good, I’ll:

1. Remove the “work in progress” language
2. Move test-related content into CONTRIBUTING.md
3. Leave this page as a lightweight developer reference

Let me know if you’d prefer a different split before I push the changes.

[JoeZiminski]

Hi @Sushma-1706 sounds great, cheers!

[Sushma-1706]

Following your suggestion, I’ve refined the developer page into a stable
reference focused on code and TUI conventions, and moved all testing-related
guidance into CONTRIBUTING.md to address #661.