Migrate gateway service from Vert.x 3.6 to Quarkus 3

[blues-man]

Summary

• Full framework migration from Eclipse Vert.x 3.6.3 (Red Hat) to Quarkus 3.17.8
• Replaces GatewayVerticle (RxJava 2 reactive) with GatewayResource (JAX-RS + Mutiny)
• Updates build tooling (Maven), Dockerfiles (UBI8/JDK17), and Kubernetes manifests

What changed

Area	Before (Vert.x)	After (Quarkus 3)
Entry point	GatewayVerticle extends AbstractVerticle	GatewayResource with @Path/@ApplicationScoped
Reactive	RxJava 2 (Single, Observable)	Mutiny (Uni, Multi)
HTTP client	Vert.x WebClient	@RegisterRestClient interfaces
Routing	Router.router(vertx)	JAX-RS @GET/@Path annotations
Config	ConfigRetriever + env vars	application.properties + MicroProfile Config
Health	Manual /health endpoint	MicroProfile @Readiness at /q/health
JSON	Vert.x JsonObject/JsonArray	POJOs with Jackson auto-serialization
Logging	SLF4J + JDK14	JBoss Logging (Quarkus built-in)
Build	vertx-maven-plugin + fabric8	quarkus-maven-plugin
Java	11	17
Docker	UBI8/OpenJDK 11	UBI8/OpenJDK 17

Files changed

• pom.xml — Quarkus 3 BOM and dependencies
• GatewayResource.java — New JAX-RS resource (replaces GatewayVerticle)
• CatalogService.java / InventoryService.java — REST client interfaces
• Product.java / Availability.java — POJO models
• GatewayHealthCheck.java — MicroProfile Health readiness check
• application.properties — Quarkus configuration
• Dockerfile / Dockerfile.multi — Updated for Quarkus + JDK 17
• kubernetes/gateway-vertx.yaml — Updated health probes and labels

Test plan

• mvn compile passes
• mvn package produces target/quarkus-app/quarkus-run.jar
• Verify /api/products returns aggregated catalog+inventory data
• Verify /q/health/ready returns health status
• Verify CORS headers present on responses
• Verify env var overrides work (COMPONENT_CATALOG_HOST, etc.)

Closes #1, #2, #3, #4, #5, #6, #7, #8

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