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/ErrorHandling.java

@@ -0,0 +1,34 @@
+///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.events.*;
+import com.github.copilot.sdk.json.*;
+import java.util.concurrent.ExecutionException;
+
+public class ErrorHandling {
+    public static void main(String[] args) {
+        try (var client = new CopilotClient()) {
+            client.start().get();
+
+            var session = client.createSession(
+                new SessionConfig()
+                    .setOnPermissionRequest(PermissionHandler.APPROVE_ALL)
+                    .setModel("gpt-5")).get();
+
+            session.on(AssistantMessageEvent.class,
+                msg -> System.out.println(msg.getData().content()));
+
+            session.sendAndWait(
+                new MessageOptions().setPrompt("Hello!")).get();
+
+            session.close();
+        } catch (ExecutionException ex) {
+            System.err.println("Error: " + ex.getCause().getMessage());
+            ex.getCause().printStackTrace();
+        } catch (Exception ex) {
+            System.err.println("Error: " + ex.getMessage());
+            ex.printStackTrace();
+        }
+    }
+}