starship: disable the docker_context module

[celkins]

Summary

Disables Starship's docker_context module. It renders whenever the Docker context is anything other than default, which under Colima is effectively always — so it becomes a permanent prompt segment that conveys nothing.

Test plan

• starship print-config parses and reports disabled = true for the module
• Confirm the segment is gone in a Docker/Colima project (not verifiable here — Docker isn't running on this machine, so the module produced no output either way)

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