Slice 1 of M7 #352 added Server.DataDir but left it un-populated —
the playlist cover-collage writer would have used "" as the relative
path root in production, writing to the current working directory.
- Add Storage.DataDir to Config (yaml: storage.data_dir, env:
SMARTMUSIC_STORAGE_DATA_DIR), defaulting to "./data".
- server.New takes the data dir as a parameter; main.go threads it.
- main.go MkdirAll's the directory at startup so the playlist cover
writer doesn't fail on first use with a missing parent.
- config.example.yaml documents the new section.
Existing internal/server/server_test.go constructs Server directly
without server.New, so no test fixture changes needed for that file.
Wire contextual scoring end-to-end: add ContextWeight to RecommendationConfig
(struct + Default()), fetch the user's current session vector in handleRadio
via loadCurrentSessionVector (cold-start returns Seed sentinel), and pass it
as the 6th arg to LoadCandidates so ContextualMatchScore flows into Shuffle.
bvandeusen