feat: add install scripts, packaging and an example plugin

install.sh places the package in a version independent directory under
XDG_DATA_HOME instead of site-packages, which would be orphaned the day
the distribution moves to a new Python. It verifies the package imports
before reporting success, and warns when the pre-split extension is still
installed alongside it.

pyproject.toml makes pip install --user an equally valid route; the
bootstrap in each plugin finds the package either way.

examples/nemoRepoLastCommit.py is a complete working plugin in sixty
lines, which is the point of the split.

uninstall.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+# Removes the installed nemoRepoCore library. The checkout and the user's
+# config file are left alone.
+set -euo pipefail
+
+dataHome="${XDG_DATA_HOME:-$HOME/.local/share}"
+installDir="$dataHome/nemo-repo-core"
+extensionsDir="$dataHome/nemo-python/extensions"
+
+if [ -e "$installDir/nemoRepoCore" ]; then
+  rm -rf "$installDir/nemoRepoCore"
+  echo "Removed $installDir/nemoRepoCore"
+else
+  echo "Nothing installed at $installDir/nemoRepoCore"
+fi
+
+rmdir "$installDir" 2>/dev/null || true
+
+remaining="$(find "$extensionsDir" -maxdepth 1 -name 'nemoRepo*.py' -o -maxdepth 1 -name 'nemoFolderTools.py' 2>/dev/null || true)"
+if [ -n "$remaining" ]; then
+  echo
+  echo "WARNING: these plugins still expect the core and will now fail to load:"
+  echo "$remaining"
+  echo "Uninstall them too, then restart Nemo with: nemo -q"
+fi