feat: mount user repo as read-only with writable shannon overlay (#273)

* feat: mount user repo as read-only with deliverables bind-mount overlay

* feat: add playground and .playwright-cli overlay mounts

* feat: add filesystem context to pipeline-testing prompts

* fix: use explicit REPO_PATH in filesystem prompt for clarity

* fix: update filesystem prompts with playground notes and absolute screenshot paths

* feat: namespace writable overlays under .shannon/ to avoid polluting host repo

* refactor: rename playground to scratchpad

* fix: redirect playwright-cli output to writable .shannon/ overlay

* fix: pre-create .shannon/ overlay mount points for Linux compatibility

* fix: exclude nested node_modules and dist from Docker build context

* fix: enforce LF line endings for shell scripts on Windows

Dockerfile

@@ -154,7 +154,7 @@ RUN ln -s /app/apps/worker/dist/scripts/save-deliverable.js /usr/local/bin/save-
     chmod +x /app/apps/worker/dist/scripts/generate-totp.js
 
 # Create directories for session data and ensure proper permissions
-RUN mkdir -p /app/sessions /app/deliverables /app/repos /app/workspaces && \
+RUN mkdir -p /app/sessions /app/repos /app/workspaces && \
     mkdir -p /tmp/.cache /tmp/.config /tmp/.npm && \
     chmod 777 /app && \
     chmod 777 /tmp/.cache && \