Add Scratch control units (if/else, wait until, repeat until)

[oco777]

Summary

• add Scratch-style If/Else, Wait Until, and Repeat Until visual scripting units under the control category
• implement coroutine-based waiting/repeat behaviors consistent with existing Scratch units
• update VS Scratch mapping documentation to list the new control units and correct categories

Testing

• not run (not requested)

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Codex Task

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Provide exit continuation from IfElseUnit branches

The new IfElseUnit only returns either ifTrue or ifFalse from OnEnter and defines no exit/control output to rejoin after the branch, so when the condition is false and the graph leaves the ifFalse port unconnected (the common case when modelling a Scratch “if/else” with an empty else), the script dead‑ends instead of continuing to the next block as Scratch does and as IfThenUnit already does with its exit output. This will halt scripts whenever the else branch is empty or not wired, diverging from Scratch control flow.

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