Add fixture-backed tests for Docker context resolution

[agustif]

Summary

The Docker resolver tests currently build their config/context data inline. That works, but it keeps the highest-risk compatibility path tied to hand-rolled test setup instead of fixture-backed layouts that resemble Docker's on-disk metadata structure.

Proposed scope

Small test-infrastructure slice for coast-docker::host:

• add file-based fixtures for Docker config/context metadata layouts
• cover:
  • DOCKER_CONTEXT
  • DOCKER_CONTEXT=default
  • DOCKER_HOST
  • config currentContext
  • TLS Storage.TLSPath
  • unsupported ssh://
• keep the tests pure and local: no live Docker engine required

Out of scope

• transport behavior changes
• daemon/CLI behavior changes
• SSH support itself

If this direction looks right, I can send a focused draft PR stacked on top of the resolver work.

[jamiesunderland]

I can take this if you want @agustif. Let me know what your plan is

[agustif]

I can take this if you want @agustif. Let me know what your plan is

hey my plan was mostly decoupling frontend from backend so it's easier to contribute to either without having to run tasks etc of both. But not sure if that fits your goals with the project, since you guys are mostly working on all of it maybe it is indeed more comfortable to you have this tied up together as it is where the frontend gets bundled into the backend and served from there?

I'll think a bit more about this and let you know jamie