Add Java MCP Server Development collection (#329)

* Add Java MCP Server Development collection

- Add Java MCP server best practices instruction
- Add Java MCP server project generator prompt
- Add Java MCP expert chat mode
- Add Java MCP development collection manifest
- Update category READMEs

Features:
- Server setup with official MCP Java SDK
- Tool/resource/prompt handlers with reactive streams
- Project Reactor for async processing
- Spring Boot integration with starters
- Stdio and HTTP transport support
- JSON schema construction with fluent builders
- Synchronous facade for blocking use cases
- Maven and Gradle build configurations

* Fix Java MCP generator prompt

- Add missing import statements for handler classes
- Add handler registration in test server setup

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Co-authored-by: Aaron Powell <me@aaron-powell.com>

collections/java-mcp-development.collection.yml

@@ -0,0 +1,35 @@
+id: java-mcp-development
+name: Java MCP Server Development
+description: 'Complete toolkit for building Model Context Protocol servers in Java using the official MCP Java SDK with reactive streams and Spring Boot integration.'
+tags: [java, mcp, model-context-protocol, server-development, sdk, reactive-streams, spring-boot, reactor]
+items:
+  - path: instructions/java-mcp-server.instructions.md
+    kind: instruction
+  - path: prompts/java-mcp-server-generator.prompt.md
+    kind: prompt
+  - path: chatmodes/java-mcp-expert.chatmode.md
+    kind: chat-mode
+    usage: |
+      recommended
+
+      This chat mode provides expert guidance for building MCP servers in Java.
+
+      This chat mode is ideal for:
+      - Creating new MCP server projects with Java
+      - Implementing reactive handlers with Project Reactor
+      - Setting up stdio or HTTP transports
+      - Debugging reactive streams and error handling
+      - Learning Java MCP best practices with the official SDK
+      - Integrating with Spring Boot applications
+
+      To get the best results, consider:
+      - Using the instruction file to set context for Java MCP development
+      - Using the prompt to generate initial project structure
+      - Switching to the expert chat mode for detailed implementation help
+      - Specifying whether you need Maven or Gradle
+      - Providing details about what tools or functionality you need
+      - Mentioning if you need Spring Boot integration
+
+display:
+  ordering: manual
+  show_badge: true