refactor(ai-core): typesafe handlers decoupled from service impl

[Schmarvinius]

1. Remove AICoreServiceImpl field from AbstractCrudHandler / all handlers. Obtain the service reference from EventContext at invocation time instead.
2. Replace string-literal event names ("resourceGroupForTenant", "stop", etc.) with compile-safe constants either generated via CDS build (cds4j generated event context interfaces) or declared as String constants on the interface/entity.
3. Switch to typesafe handler APIs: define typed EventContext subinterfaces for each action (e.g., ResourceGroupForTenantContext, StopDeploymentContext) so handlers declare typed parameters instead of doing Map extraction from context.get("data").
4. Verify that DeploymentHandler, ResourceGroupHandler, ConfigurationHandler, MockEntityHandler, and AICoreApplicationServiceHandler are also decoupled.

[github-actions]

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[Schmarvinius]

Additional review feedback from PR #49

• DEFAULT_NAME naming: Should follow standard CAP pattern: "AICoreService$Default" (Service$Default is standard for CAP-provided services)
• Decouple handlers from service impl: Handlers are registered to concrete services and the called service is always propagated via EventContext. No need to store the ServiceImpl as a reference — handler should be fully decoupled from the concrete service implementation.
• Compile-safe event names: Replace string-literal event names with constants (the constant is compile-safe).
• Typesafe handler APIs: Switch to typed EventContext subinterfaces (e.g. see cds-feature-auditlog-v2 AuditLogV2Handler)
• @After on AICoreSetupHandler: Should use @After annotation instead of current approach.
• Actions in handlers, not service impl: All implemented actions should be in handlers (same for mock variant), not in the service implementation directly.