build(docker): pin onnxruntime threads in the image

OMP_NUM_THREADS=4 capped torch in the old image, but FastEmbed runs on
onnxruntime, which ignores it and sizes its pool to the host's core count.
A CPU-limited container still reports every host core, so embedding ran with
64 threads on a 4-CPU sandbox and took up to 12x longer per file. The image
now sets EMBEDDINGS_THREADS=4 next to the existing caps; the settings guide
documents the knob.

application/Dockerfile

@@ -143,10 +143,14 @@ RUN mkdir -p /app/application/inputs/local /app/inputs /app/indexes /app/vectors
 
 ENV FLASK_APP=app.py
 
+# Thread caps. onnxruntime (FastEmbed) ignores OMP_NUM_THREADS and sizes its
+# pool to the host's core count, which a CPU-limited container still reports;
+# EMBEDDINGS_THREADS pins it the way OMP_NUM_THREADS pinned torch before.
 ENV MALLOC_ARENA_MAX=2 \
     OMP_NUM_THREADS=4 \
     MKL_NUM_THREADS=4 \
-    OPENBLAS_NUM_THREADS=4
+    OPENBLAS_NUM_THREADS=4 \
+    EMBEDDINGS_THREADS=4
 
 EXPOSE 7091