refactor: move agent Dockerfiles into their contrib directories

Dockerfile.claude and Dockerfile.codex move from the repo root into
bot_bottle/contrib/claude/Dockerfile and bot_bottle/contrib/codex/Dockerfile
respectively, so all per-provider assets live alongside the provider code.

Closes #215

bot_bottle/contrib/codex/Dockerfile

@@ -0,0 +1,28 @@
+# bot-bottle Codex provider image.
+#
+# Mirrors the default Claude image shape: Node LTS, git/network tooling,
+# non-root node user, and the provider CLI installed globally.
+
+FROM node:22-slim
+
+RUN apt-get update \
+  && apt-get install -y --no-install-recommends git ca-certificates curl \
+  && rm -rf /var/lib/apt/lists/*
+
+# App-specific deps. Python isn't required by codex itself
+# (codex is a Node CLI), but is convenient for the agent to shell
+# out to for ad-hoc scripts. Kept on its own layer so it can be
+# moved to a downstream image if the base ever needs to shrink.
+RUN apt-get update \
+  && apt-get install -y --no-install-recommends python3 python3-pip python3-venv \
+  && rm -rf /var/lib/apt/lists/*
+
+RUN npm install -g --no-fund --no-audit @openai/codex@0.136.0 \
+  && npm cache clean --force
+
+USER node
+WORKDIR /home/node
+
+RUN mkdir -p /home/node/.codex
+
+CMD ["codex"]