docs(readme): specify Everblush single dark theme

[eshanized]

Updates the Terminal UI section in the README to correctly refer to the "Everblush single dark theme" rather than the generic "M31A dark theme".

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PR created automatically by Jules for task 4655765767960415047 started by @eshanized

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Summary by cubic

Update the README to state the Terminal UI uses the Everblush single dark theme (not the M31A dark theme). Remove the missing M31A.wiki submodule to stop CI failures.

^{Written for commit 4cab0ef. Summary will update on new commits.}

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[cubic-dev-ai]

No issues found across 1 file

_{Re-trigger cubic}