The in-memory proposition store embeds with the host's embedding service too

[jasperblues]

The in-memory proposition store ignored the host's embedding service and always used the platform default. Found by reading the autoconfiguration while checking which embedder me's memory uses; not an observed failure. Closes #118.

Before

• Graph store: the host's unique or @Primary EmbeddingService, else the platform default.
• In-memory store: always ai.withDefaultEmbeddingService(), whatever the host provides.
• Nothing at startup said which embedder either store holds.

Now

• Both stores resolve through storeEmbeddingService: the host's unique or @Primary bean, else the platform default.
• Startup logs graph proposition store embeds with '<name>' (<provider>): the application's EmbeddingService bean (or the platform default embedding service).

Not changed, and why: #118 proposed failing at startup when there are several embedding beans and no @Primary. That is the ordinary case: the platform registers one bean per model it can reach (an OpenAI key alone registers three), and picking among them is what default-embedding-model is for. Failing there would break every host that doesn't register its own. The KDoc on embeddingService now says so.

Key change

fun inMemoryPropositionRepository(ai: Ai, embeddingServices: ObjectProvider<EmbeddingService>): PropositionRepository =
    InMemoryPropositionRepository(storeEmbeddingService("in-memory", ai, embeddingServices))

PropositionStoreEmbeddingServiceTest fails on main (the host's @Primary service is never called) and passes here.