[Task] Velocity Playground: Angular implementation + backend wiring

[hmoreras]

Goal

Ship the Angular Velocity Playground portlet end-to-end — UI, portlet.xml registration, and rollback toggle — in a single PR.

Frontend scope

New Nx library: core-web/libs/portlets/dot-velocity-playground/

• dot-velocity-playground-shell.component.ts
• dot-velocity-playground-page.component.ts
• lib.routes.ts exported as dotVelocityPlaygroundRoutes
• SignalStore: DotVelocityPlaygroundStore
• Data-access service: core-web/libs/data-access/src/lib/dot-velocity-playground/dot-velocity-playground.service.ts calling POST /api/vtl/dynamic/
• PrimeNG: p-splitter, Monaco editor (Velocity / VTL language mode), output panel that renders JSON, XML, and plain text outputs distinctly
• History affordance equivalent to the legacy dropdown (scope and storage location finalized by the spike — default: last 10 entries in localStorage)
• Tests: Jest + Spectator for shell / page / store with data-testid selectors on all interactive elements

Backend wiring

dotCMS/src/main/webapp/WEB-INF/portlet.xml:

• Replace the JSP-backed velocity_playground portlet with the new Angular shell.
• Add a velocity_playground-legacy entry pointing at the existing JSP as the rollback escape hatch.
• Add the corresponding PortletID enum entry and i18n key (or reuse the existing velocity_playground key).
• Live toggle so admins can revert to the JSP without redeploy.

Inputs

• Spike output from the consolidated audit issue (parity matrix + API audit + UI sketch).
• Portlet conventions: core-web/libs/portlets/CLAUDE.md.

Definition of Done

Every Gherkin scenario in epic #34737's Definition of Done passes manually against the local build:

• Admin runs valid Velocity code
• Output renders JSON, XML, and plain text
• Velocity error surfaces inline
• History recall
• Resizable split-pane
• Non-admin role is blocked
• Unlicensed instance blocks the portlet
• Rollback to legacy JSP without redeploy