[v2.0] Stop reading OmopEmbConfig deep inside EmbeddingClient and resolve_backend

[nicoloesch]

• Fixes Refactor: remove config reads from property getters and factory functions #45

OmopEmbConfig.get_config() was being called deep inside EmbeddingClient's constructor/embedding_dim property and inside resolve_backend(), instead of once at CLI entry points. Two of the three call sites silently swallowed config errors (except FileNotFoundError / bare except Exception) rather than surfacing misconfiguration. Config is now resolved exactly once per CLI command and threaded down as plain arguments:

• EmbeddingClient gains embedding_dim, document_embedding_prefix, query_embedding_prefix constructor parameters; property getters no longer read config internally.
• resolve_backend(backend_type, *, sqlite_path=None) no longer reads config at all; a new resolve_backend_from_config(cfg) is the one place backend selection touches OmopEmbConfig.
• New load_omop_emb_config() also catches ConfigurationError (missing required resource), previously uncaught anywhere and left to propagate as a raw ValueError.

[gkennos]

configuration.md and interface_guide.md still show resolve_backend with no args

docs should switch to load_omop_emb_config() + resolve_backend_from_config(cfg), or show explicit resolve_backend with new args (both since both public apis?)

[nicoloesch]

Closing in favor of absorbing this into #53 , which is already restructuring resolve_backend()/OmopEmbConfig in the same area.

The resolve_backend()/resolve_backend_from_config() split here is being adopted as designed, including the docs fix flagged in review (configuration.md/interface_guide.md). Landing together rather than as two separate breaking releases back to back.