PROMOTE: wrap the embedder BOUNDARY call + the pure schema record
builder into a Result-tracked promoter. The single caller (the
pipeline) gets one r/ok / r/err to thread through.

Why this is a promoter even though it touches the embedder:
`embed-for-entry` returns Result; from the pipeline's POV the
embedding is just data flowing through the bundle. The actual
I/O (HTTP call to Ollama) is encapsulated in the embedder ns;
here we only orchestrate.

PROMOTE: pure functions that compute relocation routing decisions
from an entry. No I/O, no embedder calls, no Milvus reads — purely
data → Result.

Used by `hive-milvus.relocate.pipeline/relocate-one` to decide
whether an entry needs to move and where it should go before any
BOUNDARY effect fires.