Chroma persist directory resolves inconsistently between host and container #8

persist_directory="./chroma_data" is a relative path, which resolves differently
depending on whether the process runs on host vs. inside Docker — caused real
confusion debugging #3, comparing what looked like the same data source but were
actually two disconnected Chroma stores.

Fix

Compute an absolute path from the source file's own location
(Path(__file__).resolve().parent.parent / "chroma_data"), removing the
ambiguity structurally rather than documenting around it.

PR: #4