Drop forge-core jackson-databind version override and let micronaut-platform manage it

Removes the explicit `:$jacksonDatabindVersion` coordinate flagged
by jdaugherty in PR #15365 review on grails-forge-core/build.gradle:51.
The micronaut-platform 4.10.10 BOM (already imported as a platform on
the line above) imports jackson-bom transitively, which manages
jackson-databind. Verified with `gradle :grails-forge-core:dependencies
--configuration compileClasspath` -> `com.fasterxml.jackson.core:
jackson-databind -> 2.19.2` (one minor newer than the previously
hard-coded 2.18.3).

The `jacksonDatabindVersion` property is left in
grails-forge/gradle.properties because grails-forge/buildSrc/build.gradle
still references it on its own gradle-plugin compile classpath, where
no BOM is imported.

Verified: `gradle :grails-forge-core:compileJava
:grails-forge-core:compileTestGroovy` passes.

Assisted-by: claude-code:claude-opus-4-7

Author: jamesfredley

grails-forge/grails-forge-core/build.gradle

@@ -48,7 +48,7 @@ dependencies {
     testAnnotationProcessor 'io.micronaut:micronaut-inject-java'
 
     api platform("io.micronaut.platform:micronaut-platform:$micronautVersion") // TODO: Should this be api?
-    api "com.fasterxml.jackson.core:jackson-databind:$jacksonDatabindVersion"
+    api 'com.fasterxml.jackson.core:jackson-databind'
     api 'jakarta.validation:jakarta.validation-api'
     api "com.fizzed:rocker-runtime:$rockerVersion"
     api "io.github.java-diff-utils:java-diff-utils:$javaDiffUtils"