fix(linux): install SVG icon to XDG hicolor theme so "Open with" shows the icon

The .desktop file used a named icon (Icon=io.github.HakanSeven12.OpenCadStudio)
but the icon file was never written to the XDG icon theme directory, so file
managers and the "Open with" picker fell back to a generic blank document icon.

install_icon() now writes assets/logo.svg (embedded at compile time) to
~/.local/share/icons/hicolor/scalable/apps/{APP_ID}.svg alongside the
.desktop file, and runs gtk-update-icon-cache so the change is picked up
immediately. The write is skipped when the on-disk file is already identical.

https://claude.ai/code/session_01DFVSKgViFaxEjZD2KsTdtt

src/io/file_association.rs

@@ -367,6 +367,9 @@ mod linux_impl {
 
         std::fs::create_dir_all(&apps).map_err(|e| e.to_string())?;
         std::fs::write(&desktop_path, &contents).map_err(|e| e.to_string())?;
+
+        install_icon()?;
+
         // Best-effort: refresh the MIME→app cache. Absent on minimal systems.
         let _ = std::process::Command::new("update-desktop-database")
             .arg(&apps)
@@ -374,6 +377,34 @@ mod linux_impl {
         Ok(())
     }
 
+    /// Write the app SVG icon into the user's hicolor icon theme so that the
+    /// named `Icon={APP_ID}` entry in the .desktop file resolves correctly in
+    /// file managers and the "Open with" picker. Skipped when the icon is
+    /// already up-to-date; best-effort icon-cache refresh afterwards.
+    fn install_icon() -> Result<(), String> {
+        static LOGO_SVG: &[u8] = include_bytes!("../../assets/logo.svg");
+
+        let icon_dir = data_home()?.join("icons/hicolor/scalable/apps");
+        let icon_path = icon_dir.join(format!("{APP_ID}.svg"));
+
+        // Skip write when the on-disk file is already identical.
+        if std::fs::read(&icon_path).ok().as_deref() == Some(LOGO_SVG) {
+            return Ok(());
+        }
+
+        std::fs::create_dir_all(&icon_dir).map_err(|e| e.to_string())?;
+        std::fs::write(&icon_path, LOGO_SVG).map_err(|e| e.to_string())?;
+
+        // Refresh the icon cache so desktop environments pick up the new file.
+        let hicolor = data_home()
+            .map(|d| d.join("icons/hicolor"))
+            .unwrap_or_default();
+        let _ = std::process::Command::new("gtk-update-icon-cache")
+            .args(["--force", "--quiet", &hicolor.to_string_lossy()])
+            .status();
+        Ok(())
+    }
+
     fn data_home() -> Result<PathBuf, String> {
         std::env::var_os("XDG_DATA_HOME")
             .map(PathBuf::from)