fix(docker): install python-is-python3 so bare python resolves in containers

Debian 13 ships only `python3` — there's no `/usr/bin/python` symlink. When
the agent emits bash commands using bare `python` (which models do frequently
from their training prior), every such call fails with:

    /usr/bin/bash: python: command not found
    Tool terminal returned error … exit_code 127

The agent then retries with different approaches, sessions take longer, and
agent.log fills with WARNING noise.

`python-is-python3` is the standard Debian package that drops a
`/usr/bin/python → python3` symlink. ~30 KB, zero behavior change for
anything calling `python3` directly; transparent fix for everything else.

Fixes #33178.

Dockerfile

@@ -25,7 +25,7 @@ ENV PLAYWRIGHT_BROWSERS_PATH=/opt/hermes/.playwright
 # hermes process, the dashboard, and per-profile gateways.
 RUN apt-get update && \
     apt-get install -y --no-install-recommends \
-    ca-certificates curl python3 ripgrep ffmpeg gcc python3-dev libffi-dev procps git openssh-client docker-cli xz-utils && \
+    ca-certificates curl python3 python-is-python3 ripgrep ffmpeg gcc python3-dev libffi-dev procps git openssh-client docker-cli xz-utils && \
     rm -rf /var/lib/apt/lists/*
 
 # ---------- s6-overlay install ----------