revert Jackson BOM and lock at 2.19.2 due to OpenAI lib

Author: docwho2

pom.xml

@@ -86,7 +86,10 @@
             <dependency>
                 <groupId>com.fasterxml.jackson</groupId>
                 <artifactId>jackson-bom</artifactId>
-                <version>2.20.0</version>
+                <!-- Pinned at 2.19.2 because OpenAI client 0.18.2 still references
+                PropertyNamingStrategy.SNAKE_CASE (removed in 2.20.0). 
+                TODO: update once legacy OpenAI lib is retired. -->
+                <version>2.19.2</version>
                 <type>pom</type>
                 <scope>import</scope>
             </dependency>