Support task string shorthand and command string[] shorthand

[crusty-voidzero]

Summary

Implement the two config simplifications discussed in Discord:

1. Allow task shorthand:
   • "some-task": "... command"
   • equivalent to "some-task": { "command": "... command" }
2. Allow command to accept string[] as a shorthand for sequential commands / current && style composition.

Notes

• The task string shorthand should keep the same default caching behavior as the object form (run.cache still overrides, default remains true).
• This issue intentionally does not include commands directly inside dependsOn; that was called out as more complex and should be considered separately with concurrency-control / unnamed-task design.
• Docs should make sequencing semantics explicit where relevant.
• These two shorthands can be combined: "some-task": ["cmd1", "cmd2"]