developer_migrate: the final clamp truncated every float to 0

clamp() applied to the bare point() read with integer bounds resolves
to the integer clamp, so 0.5 became 0 and the growth solver emptied on
its first frame. Read the value into a float first, as the float node
did. The spike test could not see this: at full influence a lone 1
sends everything and the result is the same whether or not the point's
own value survives. The stage trace on a uniform field does.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

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