Plain units already get a gap from the source whitespace, so drop the
leading space inside the string; keep it only on superscripted units
(in^2, in^3, in^4, ft^2). Also fix the generated concrete-beam figure
labels. Regenerate all affected PDFs.
Plain unit strings already get a gap from the source whitespace, so the
added leading space doubled it; keep the leading space only on
superscripted units.
Rename calc.py locals and result keys, add inline unit comments, and
normalize Lp/Lr/Lb to feet. Update steel-beam.typ references and the
tests (current W10X15 input, --stdout summary behavior).
