📌(agents) pin Docker image to a specific tag for reproducible builds

Avoid using floating tags and pin the image to an explicit version
to ensure consistent and reproducible agent builds.

src/agents/Dockerfile

@@ -1,4 +1,4 @@
-FROM python:3.13-slim AS base
+FROM python:3.13.13-slim AS base
 
 # Install system dependencies required by LiveKit
 RUN apt-get update && apt-get install -y \