Add pinch valve support

[gitgrahamdunn]

Summary

• Add a Valve_pinch_manual_generic.csv table so manual pinch valves appear in the existing valve insertion form.
• Add a pinch-valve-specific legacy valve renderer keyed by VType containing pinch.
• Render a flanged manual pinch valve body with through bore, flexible pinched sleeve, bonnet, yoke, stem, and handwheel.
• Mark Pinch Valve complete in the README roadmap.

Catalog source and mapping

• Source: i-Flow Manual Pinch Valve dimension table.
• Catalog L (Steel) -> Quetzal Height face-to-face valve length.
• Catalog D -> Quetzal ODBody sizing hint for the body/flange diameter.
• Catalog Dg -> Quetzal ID bore diameter.
• Kv is set to 0 because the source catalog page does not publish flow coefficients.
• Included sizes: DN50, DN65, DN80, DN100, DN125, DN150, DN200, DN250, DN300.

Catalog URL:

• https://www.iflowvalves.com/proDetail/Manual-Pinch-Valve

Validation

• python3 -m py_compile pFeatures.py pCmd.py pForms.py dodoDialogs.py
• CSV validation: all pinch rows parse, PSize values are unique, dimensions are positive, Kv is non-negative, and every VType dispatches to the pinch renderer.

Notes

• This PR is based directly on origin/master and does not depend on the other open valve PRs.
• I could not generate a FreeCAD screenshot in this environment because freecadcmd/FreeCADCmd is not installed.