Add annotation-based agent API (Phase 5A)

New modules:
- acp-annotations: Zero-dependency annotation definitions (@AcpAgent, @initialize, @newSession, @prompt, @sessionid, @SessionState)
- acp-agent-support: Reflection-based runtime for annotation processing

Key components:
- ArgumentResolver pattern with caching (Spring MVC-style)
- ReturnValueHandler pattern for flexible return types
- InterceptorChain with proper lifecycle tracking
- AcpAgentSupport bootstrap class

Features:
- String return auto-converts to PromptResponse.text()
- void return auto-converts to PromptResponse.endTurn()
- Flexible parameter injection (request, context, capabilities)

Validated by BuilderVsAnnotationComparisonTest showing:
- 40% boilerplate reduction for basic lifecycle
- 50% reduction for file operations
- 60% reduction for terminal execution

Author: Mark Pollack

acp-agent-support/pom.xml

@@ -0,0 +1,60 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>com.agentclientprotocol</groupId>
+        <artifactId>acp-java-sdk</artifactId>
+        <version>0.9.0-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>acp-agent-support</artifactId>
+    <name>ACP Agent Support</name>
+    <description>Reflection-based runtime for annotation-driven ACP agents</description>
+
+    <dependencies>
+        <!-- ACP dependencies -->
+        <dependency>
+            <groupId>com.agentclientprotocol</groupId>
+            <artifactId>acp-annotations</artifactId>
+            <version>${project.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.agentclientprotocol</groupId>
+            <artifactId>acp-core</artifactId>
+            <version>${project.version}</version>
+        </dependency>
+
+        <!-- Logging -->
+        <dependency>
+            <groupId>org.slf4j</groupId>
+            <artifactId>slf4j-api</artifactId>
+        </dependency>
+
+        <!-- Test dependencies -->
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>ch.qos.logback</groupId>
+            <artifactId>logback-classic</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.agentclientprotocol</groupId>
+            <artifactId>acp-test</artifactId>
+            <version>${project.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+</project>