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/README.md

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+# Runnable Recipe Examples
+
+This folder contains standalone, executable Java examples for each cookbook recipe. Each file can be run directly with [JBang](https://www.jbang.dev/) — no project setup required.
+
+## Prerequisites
+
+- Java 17 or later
+- JBang installed:
+
+```bash
+# macOS (using Homebrew)
+brew install jbangdev/tap/jbang
+
+# Linux/macOS (using curl)
+curl -Ls https://sh.jbang.dev | bash -s - app setup
+
+# Windows (using Scoop)
+scoop install jbang
+```
+
+For other installation methods, see the [JBang installation guide](https://www.jbang.dev/download/).
+
+## Running Examples
+
+Each `.java` file is a complete, runnable program. Simply use:
+
+```bash
+jbang <FileName>.java
+```
+
+### Available Recipes
+
+| Recipe               | Command                              | Description                                |
+| -------------------- | ------------------------------------ | ------------------------------------------ |
+| Error Handling       | `jbang ErrorHandling.java`           | Demonstrates error handling patterns       |
+| Multiple Sessions    | `jbang MultipleSessions.java`        | Manages multiple independent conversations |
+| Managing Local Files | `jbang ManagingLocalFiles.java`      | Organizes files using AI grouping          |
+| PR Visualization     | `jbang PRVisualization.java`         | Generates PR age charts                    |
+| Persisting Sessions  | `jbang PersistingSessions.java`      | Save and resume sessions across restarts   |
+| Ralph Loop           | `jbang RalphLoop.java`              | Autonomous AI task loop                    |
+| Accessibility Report | `jbang AccessibilityReport.java`     | WCAG accessibility report generator        |
+
+### Examples with Arguments
+
+**PR Visualization with specific repo:**
+
+```bash
+jbang PRVisualization.java github/copilot-sdk
+```
+
+**Managing Local Files with specific folder:**
+
+```bash
+jbang ManagingLocalFiles.java /path/to/your/folder
+```
+
+**Ralph Loop in planning mode:**
+
+```bash
+jbang RalphLoop.java plan 5
+```
+
+## Why JBang?
+
+JBang lets you run Java files as scripts — no `pom.xml`, no `build.gradle`, no project scaffolding. Dependencies are declared inline with `//DEPS` comments and resolved automatically.
+
+## Learning Resources
+
+- [JBang Documentation](https://www.jbang.dev/documentation/guide/latest/)
+- [GitHub Copilot SDK for Java](https://github.com/github/copilot-sdk-java)
+- [Parent Cookbook](../README.md)