Add Java SDK cookbook with 7 recipes

Add complete Java cookbook matching the pattern of existing .NET, Go,
Node.js, and Python cookbooks. All 7 recipes included:

- Ralph Loop: Autonomous AI task loops with JBang
- Error Handling: try-with-resources, ExecutionException, timeouts
- Multiple Sessions: Parallel sessions with CompletableFuture
- Managing Local Files: AI-powered file organization
- PR Visualization: Interactive PR age charts
- Persisting Sessions: Save/resume with custom IDs
- Accessibility Report: WCAG reports via Playwright MCP

Each recipe includes both markdown documentation and a standalone
JBang-runnable Java file in recipe/.

cookbook/copilot-sdk/java/recipe/MultipleSessions.java

@@ -0,0 +1,37 @@
+///usr/bin/env jbang "$0" "$@" ; exit $?
+//DEPS com.github:copilot-sdk-java:0.2.1-java.1
+
+import com.github.copilot.sdk.*;
+import com.github.copilot.sdk.json.*;
+import java.util.concurrent.CompletableFuture;
+
+public class MultipleSessions {
+    public static void main(String[] args) throws Exception {
+        try (var client = new CopilotClient()) {
+            client.start().get();
+
+            var config = new SessionConfig()
+                .setModel("gpt-5")
+                .setOnPermissionRequest(PermissionHandler.APPROVE_ALL);
+
+            // Create 3 sessions in parallel
+            var f1 = client.createSession(config);
+            var f2 = client.createSession(config);
+            var f3 = client.createSession(new SessionConfig()
+                .setModel("claude-sonnet-4.5")
+                .setOnPermissionRequest(PermissionHandler.APPROVE_ALL));
+            CompletableFuture.allOf(f1, f2, f3).get();
+
+            var s1 = f1.get(); var s2 = f2.get(); var s3 = f3.get();
+
+            // Send a message to each session
+            System.out.println("S1: " + s1.sendAndWait(new MessageOptions().setPrompt("Explain Java records")).get().getMessage());
+            System.out.println("S2: " + s2.sendAndWait(new MessageOptions().setPrompt("Explain sealed classes")).get().getMessage());
+            System.out.println("S3: " + s3.sendAndWait(new MessageOptions().setPrompt("Explain pattern matching")).get().getMessage());
+
+            // Clean up
+            s1.destroy().get(); s2.destroy().get(); s3.destroy().get();
+            client.stop().get();
+        }
+    }
+}