Kea3D 0.1.91 Free/Core source

Matching limited Free/Core source snapshot for the local 0.1.91 Windows and Android candidates. Includes Linux native CAD support, responsive Settings fixes, Anchor visibility and picking improvements, companion-file resolution fixes, safe manifest Save As handling, and regression tests. Clean snapshot validation passed: dependency install, lint, typecheck, 118 unit tests, production build, and bundle budget. This is a source release, not a signed production binary release. Physical Android acceptance remains pending. Source ZIP SHA-256: 088183222A5A0939FEEF1D45F92F16C81C9A05A13F7D3EE17D96B208430743CA.