feat: add live config profile refresh

- Standardize built-in tool users for shared writable profile mounts
- Mount canonical non-Git profile sources across compatible instances
- Report restart-required outcomes and guard active profile deletion
- Surface restart feedback in config profile editing

Quality gates: frontend build passed; backend py_compile and LSP passed.
Skipped: backend pytest/Ruff unavailable; Docker/manual checks not approved.

tool-images/jupyter.dockerfile

@@ -17,7 +17,10 @@ RUN apt-get update && apt-get install -y \
 # Set up git
 RUN git config --global init.defaultBranch main
 
-# Switch back to jovyan user (default for scipy-notebook)
-USER ${NB_UID}
+# start-notebook.py maps jovyan to this shared UID/GID and drops privileges.
+# Keep the image root at entrypoint time so that mapping can occur.
+ENV NB_UID=1000 \
+    NB_GID=1000
+USER root
 
 EXPOSE 8888