BaseEmbedderConfig baked "http://localhost:1234/v1" into the
lmstudio_base_url default, so the attribute was never falsy and the
embedder had no way to tell "unset" from "explicitly localhost". Setting
LMSTUDIO_BASE_URL had no effect.
The default moves to the provider, which now resolves explicit config,
then LMSTUDIO_BASE_URL, then the localhost default, matching how the
OpenAI embedder already reads OPENAI_BASE_URL. The resolved value is
written back to config.lmstudio_base_url, so the attribute still reads
the same after construction.
Closes#6692
kartik-mem0
08e9cc476c