Consolidate the `/spark` command into `/roll` to simplify the CLI.
The `/roll` command now handles both dice notation and spark table
slugs.
- Update `parseInput` to treat `/roll` arguments as a generic string.
- Update `dispatchCommand` to check for spark table matches before
evaluating dice notation or variable expressions.
- Update command completions to show both dice and spark table
suggestions under `/roll`.
- Update documentation and UI placeholders to reflect the change.
hypercross
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