[Bug]: Inconsistent definition of TaskState

### What happened?

In https://a2a-protocol.org/latest/specification/#413-taskstate, the `TaskState` enum is defined in all caps using the `TASK` suffix, which breaks compatibility with version 0.3.0.

However, the examples at https://a2a-protocol.org/latest/specification/#6-common-workflows-examples all show the state in the lower kebab case, just like it was in v0.3.0.

Either the `TaskState` or examples are wrong, please clarify which.

Thanks

### Relevant log output

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