fix(stack): no docker fallback in native mode

[7ttp]

TL;DR

Fixes mode: "native" silently falling back to Docker when native binary resolution fails.
The fallback was mode blind
a BinaryNotFoundError or DownloadError always resolved to a Docker image, so a 404 on a native release quietly switched the service to Docker and hid whatever was actually broken. Mode is now threaded into resolution: "native" fails with the error, "auto" falls back exactly like before, "docker" untouched...

Since these errors can actually reach the user now, they also got real messages
(which service, which platform, which URL, and a hint to use auto/docker) instead of printing a bare BinaryNotFoundError nothing downstream needed changing since everything already reads message...

refs

• closes stack: mode: "native" silently falls back to Docker when binary resolution fails #5787

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