feat: tenant scoping & multi-tenancy property alignment

[Schmarvinius]

Scope: correctness + config naming.

• Restrict AICore.resourceGroups, AICore.deployments, AICore.configurations reads/deletes to the current tenant (no leakage across tenants).
• Replace cds.requires.AICore.multiTenancy with the standard cds.multiTenancy.* (https://pages.github.tools.sap/cap/docs/java/developing-applications/properties#cds-multiTenancy).
• Rename namespace cds.requires.AICore.* → cds.ai.core.* to follow CAP Java property convention.
• Make FioriRecommendationHandler.entitiesWithoutPredictions cache tenant-keyed and register a handler on the extensibility service MODEL_CHANGED event to invalidate it. Also explain who actually populates the cache (or remove the dead/incomplete logic).

[github-actions]

👋 Hello @Schmarvinius, thank you for submitting this issue. Our team is reviewing your report and will follow up with you as soon as possible.