Unscoped create or modify translations writes into Marketplace modules; theme create --from seeds the dark palette with light colours #970

From the JTSBootLogboek page redesign (re-verified on main 0cac362).

1. Unscoped create or modify translations writes into Marketplace modules and Atlas templates.
   • It is keyed on the source text across the whole project (documented). On TestApp, 'Cancel' as 'Annuleren' set 50 translations in 38 documents, including WorkflowCommons, Administration, FeedbackModule, Atlas building blocks and page templates.
   • The next module update overwrites those changes, and they show up as unexpected diffs.
   • Fix: by default skip Marketplace modules and page templates/building blocks, and report how many occurrences were skipped. Add an explicit opt-in to include them. At minimum, warn.
   • Code: mdl/executor/cmd_translations.go:20-23 (translationScope).
2. theme create --from with a design that has only a base palette seeds the dark variant with light colours.
   • --mxt-brand, --mxt-ground: #f7f9fb and --mxt-ink: #1b2733 overwrite the dark mixin while its surfaces stay dark, which gives an unreadable mixed palette.
   • Cause: cmd/mxcli/theme/tokens.go:72-87 (forVariant), used at create.go:398.
   • Fix: when the design has no block for a variant, leave that variant's mixin alone (or seed only non-colour tokens), and print a note.
   • Cosmetic: the first injected token lands on the @mixin … { line, unindented.
   • (The }} part of the report was already fixed in 8052f61.)