chore: rename H7CAD to Open CAD Studio

Joining the OpenAEC Foundation (open-aec.com). Crate/struct become
OpenCADStudio, user-facing strings use the spaced "Open CAD Studio"
form, repo URLs point to HakanSeven12/open-cad-studio. Logo (window
icon + assets/logo.svg) redrawn with OCS initials. Drop examples/
binaries — unused.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/io/pdf_export.rs

@@ -78,7 +78,7 @@ fn build_pdf(
     rotation_deg: i32,
     plot_style: Option<&PlotStyleTable>,
 ) -> Vec<u8> {
-    let mut doc = PdfDocument::new("H7CAD Export");
+    let mut doc = PdfDocument::new("Open CAD Studio Export");
     let mut ops: Vec<Op> = Vec::new();
 
     // White page background.