Add Linux platform with .desktop file generation

Implements LinuxPlatform to handle Linux-specific desktop integration.
Creates .desktop files in ~/.local/share/applications/ for proper
application integration including:

- Application launcher in desktop menus
- Application icon display
- Executable path configuration
- MimeType field for URI scheme registration (via scijava-links)

Configuration via system properties:
- scijava.app.name: Application name
- scijava.app.executable: Path to executable
- scijava.app.icon: Icon file path
- scijava.app.directory: Working directory
- scijava.app.desktop-file: .desktop file path (auto-set if not provided)

The LinuxPlatform creates the basic .desktop file structure, and
scijava-links later modifies it to add URI scheme handlers.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: ctrueden

src/main/java/org/scijava/desktop/platform/linux/LinuxPlatform.java

@@ -0,0 +1,212 @@
+/*
+ * #%L
+ * Desktop integration for SciJava.
+ * %%
+ * Copyright (C) 2010 - 2026 SciJava developers.
+ * %%
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * 
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * #L%
+ */
+
+package org.scijava.desktop.platform.linux;
+
+import org.scijava.log.LogService;
+import org.scijava.platform.AbstractPlatform;
+import org.scijava.platform.Platform;
+import org.scijava.platform.PlatformService;
+import org.scijava.plugin.Parameter;
+import org.scijava.plugin.Plugin;
+
+import java.io.BufferedWriter;
+import java.io.IOException;
+import java.net.URL;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+
+/**
+ * A platform implementation for handling Linux platform issues.
+ * <p>
+ * This implementation creates and maintains a .desktop file for the application,
+ * enabling proper desktop integration including:
+ * </p>
+ * <ul>
+ * <li>Application launcher in menus</li>
+ * <li>Application icon</li>
+ * <li>File associations (via separate configuration)</li>
+ * <li>URI scheme handling (via scijava-links)</li>
+ * </ul>
+ *
+ * @author Curtis Rueden
+ */
+@Plugin(type = Platform.class, name = "Linux")
+public class LinuxPlatform extends AbstractPlatform {
+
+	@Parameter(required = false)
+	private LogService log;
+
+	// -- Platform methods --
+
+	@Override
+	public String osName() {
+		return "Linux";
+	}
+
+	@Override
+	public void configure(final PlatformService service) {
+		super.configure(service);
+
+		// Create or update .desktop file for desktop integration
+		try {
+			installDesktopFile();
+		}
+		catch (final IOException e) {
+			if (log != null) {
+				log.error("Failed to install .desktop file", e);
+			}
+		}
+	}
+
+	@Override
+	public void open(final URL url) throws IOException {
+		if (getPlatformService().exec("xdg-open", url.toString()) != 0) {
+			throw new IOException("Could not open " + url);
+		}
+	}
+
+	// -- Helper methods --
+
+	/**
+	 * Creates or updates the .desktop file for this application.
+	 * <p>
+	 * The .desktop file path is determined by the {@code scijava.app.desktop-file}
+	 * system property. If not set, defaults to {@code ~/.local/share/applications/<app>.desktop}.
+	 * </p>
+	 */
+	private void installDesktopFile() throws IOException {
+		// Get configuration from system properties
+		String desktopFilePath = System.getProperty("scijava.app.desktop-file");
+
+		if (desktopFilePath == null) {
+			// Default location
+			final String appName = System.getProperty("scijava.app.name", "scijava-app");
+			final String home = System.getProperty("user.home");
+			desktopFilePath = home + "/.local/share/applications/" + sanitizeFileName(appName) + ".desktop";
+
+			// Set property for other components (e.g., scijava-links)
+			System.setProperty("scijava.app.desktop-file", desktopFilePath);
+		}
+
+		final Path desktopFile = Paths.get(desktopFilePath);
+
+		// Check if file already exists and is up-to-date
+		if (Files.exists(desktopFile) && isDesktopFileUpToDate(desktopFile)) {
+			if (log != null) {
+				log.debug("Desktop file is up-to-date: " + desktopFile);
+			}
+			return;
+		}
+
+		// Get application properties
+		final String appName = System.getProperty("scijava.app.name", "SciJava Application");
+		final String appExec = System.getProperty("scijava.app.executable");
+		final String appIcon = System.getProperty("scijava.app.icon");
+		final String appDir = System.getProperty("scijava.app.directory");
+
+		if (appExec == null) {
+			if (log != null) {
+				log.debug("No executable path set (scijava.app.executable property), skipping .desktop file creation");
+			}
+			return;
+		}
+
+		// Create parent directory if needed
+		final Path parent = desktopFile.getParent();
+		if (parent != null && !Files.exists(parent)) {
+			Files.createDirectories(parent);
+		}
+
+		// Write .desktop file
+		try (final BufferedWriter writer = Files.newBufferedWriter(desktopFile, StandardCharsets.UTF_8)) {
+			writer.write("[Desktop Entry]");
+			writer.newLine();
+			writer.write("Type=Application");
+			writer.newLine();
+			writer.write("Version=1.0");
+			writer.newLine();
+			writer.write("Name=" + appName);
+			writer.newLine();
+			writer.write("GenericName=" + appName);
+			writer.newLine();
+			writer.write("X-GNOME-FullName=" + appName);
+			writer.newLine();
+
+			if (appIcon != null) {
+				writer.write("Icon=" + appIcon);
+				writer.newLine();
+			}
+
+			writer.write("Exec=" + appExec + " %U");
+			writer.newLine();
+
+			if (appDir != null) {
+				writer.write("Path=" + appDir);
+				writer.newLine();
+			}
+
+			writer.write("Terminal=false");
+			writer.newLine();
+			writer.write("Categories=Science;Education;");
+			writer.newLine();
+
+			// MimeType field intentionally left empty
+			// scijava-links will add URI scheme handlers (x-scheme-handler/...)
+			writer.write("MimeType=");
+			writer.newLine();
+		}
+
+		// Make file readable (but not writable) by others
+		// This is standard practice for .desktop files
+		// Files.setPosixFilePermissions can be used here if needed
+
+		if (log != null) {
+			log.info("Created desktop file: " + desktopFile);
+		}
+	}
+
+	/**
+	 * Checks if the desktop file is up-to-date with current system properties.
+	 */
+	private boolean isDesktopFileUpToDate(final Path desktopFile) {
+		// For now, simple existence check
+		// Future: could parse and compare with current properties
+		return Files.exists(desktopFile);
+	}
+
+	/**
+	 * Sanitizes a string for use as a file name.
+	 */
+	private String sanitizeFileName(final String name) {
+		return name.replaceAll("[^a-zA-Z0-9._-]", "-").toLowerCase();
+	}
+}