fix(docker): use Python 3.13 for gensim compatibility (#1172)

Docker build was broken on python:3.14-slim because gensim doesn't ship a
3.14 wheel yet (typical of bleeding edge Python), so pip
tries to compile it from source and there's no gcc in the slim image.

gensim's a core dependency  so every build hit this.

Went back to 3.13 instead of installing a compiler : simpler, and 3.14 was
just a jump from an automated bump PR anyway.

Fixes #1025.

Dockerfile

@@ -9,7 +9,7 @@ RUN npm ci
 COPY explorer/ ./
 RUN mkdir -p /app/semantica && npm run build
 
-FROM python:3.14-slim AS runtime
+FROM python:3.13-slim AS runtime
 
 ENV PYTHONDONTWRITEBYTECODE=1 \
     PYTHONUNBUFFERED=1 \