Contract-first API with DTOs, validation, and server-side OpenAPI post-processing

Add dedicated request/response DTOs for all controllers, replacing raw
JsonNode parameters with validated types. Move OpenAPI path-prefix stripping
and ProcessorNode children injection into OpenApiCustomizer beans so the
spec served at /api/v1/api-docs is already clean — eliminating the need for
the ui/scripts/process-openapi.mjs post-processing script.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cameleer3-server-app/pom.xml

@@ -66,6 +66,10 @@
             <artifactId>org.eclipse.xtext.xbase.lib</artifactId>
             <version>2.37.0</version>
         </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-validation</artifactId>
+        </dependency>
         <dependency>
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-starter-security</artifactId>