Drops and recreates the sqlite-vec tables at the current model dimension, then
re-queues every image for embedding. Fixes "dimension mismatch" search errors
that occur when the vector table was built for a different model/dimension (e.g.
after experimenting with 768-dim models against this 512-dim build).
The rebuild runs under the embedding worker's DB write lock and resets the job
queue inside a single transaction, so it can't interleave with an in-flight
embedding batch (per code review).
LyAhn
f66fbe7931