Prepare extension for Quarkiverse migration

[t1]

Sub-issue of #28. Depends on Quarkiverse repo being created.

Prepare the extension code for migration to the new Quarkiverse repository.

Scope:

• Update Maven coordinates to io.quarkiverse.openapiui:quarkus-openapi-ui
• Add Quarkiverse parent POM
• Migrate extension modules (deployment + runtime) structure
• Update internal references and imports
• Preserve git history during migration

Completion criteria:

• Extension code ready to move to quarkiverse/quarkus-openapi-ui
• Build and tests pass with new coordinates
• Git history preserved

[t1]

Agent: starting work

Type: Feature
Summary: Prepare the Quarkus extension code for migration to the Quarkiverse ecosystem. This involves updating Maven coordinates, adjusting the POM structure to use the Quarkiverse parent, and ensuring the extension is self-contained and ready to move to its own repository.

Design decisions:

• New coordinates: io.quarkiverse.openapiui:quarkus-openapi-ui (group + artifact change)
• Use Quarkiverse parent POM for release management and ecosystem integration
• Keep deployment + runtime module structure (standard Quarkus extension pattern)
• Preserve all existing functionality — this is a packaging change, not a behavioral change
• Stay in this repo until the Quarkiverse repo is created (no external coordination needed for preparation)

Acceptance criteria:

• Maven coordinates updated to io.quarkiverse.openapiui:quarkus-openapi-ui-*
• POMs reference Quarkiverse parent
• Build and tests pass with new coordinates
• Extension remains compatible with existing users (version continuity)

Files:

• quarkus-extension/pom.xml
• quarkus-extension/deployment/pom.xml
• quarkus-extension/runtime/pom.xml
• Any internal references to the old coordinates