Update onyx usage docs.

[jasperblues]

Summary

• Document @DependsOn requirement when directly injecting model beans (EmbeddingService, LlmService) registered via registerSingleton
• Update ProviderInitialization KDoc to explain the dynamic registration pattern and its implications for consumers
• Update RAG reference docs with @DependsOn in the DrivineStore code examples (Java and Kotlin)

Context

Model provider auto-configurations register beans dynamically via ConfigurableBeanFactory.registerSingleton() to support multiple models per provider with configuration-driven names. This is invisible to most consumers since framework beans like ModelProvider handle ordering internally.
However, application code that injects EmbeddingService or LlmService directly (e.g. wiring a custom DrivineStore) will get a NoSuchBeanDefinitionException without @DependsOn, because Spring resolves the dependency before the initializer's factory method has run.

Discovered while integrating the ONNX embedding module in embabel/guide.

Changes

File	Change
embabel-agent-common/embabel-agent-ai/.../ProviderInitialization.kt	Expanded KDoc: explains registerSingleton pattern, when @DependsOn is needed, and why
embabel-agent-docs/.../reference/rag/page.adoc	Added @DependsOn("onnxEmbeddingInitializer") to Java and Kotlin examples; added NOTE explaining the requirement

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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