refactor: rebuild as an emblem plugin on nemo-repo-core

Everything that was not about drawing emblems moves out: the columns, the properties tab and the context menu are their own plugins now, and the config, git and cache layers come from nemo-repo-core.

The indicator list stops being hardcoded. Entries that are not one of the three git derived indicators are matched by marker_directory or marker_file, which is how claude_dir now works and how a user adds their own without touching the code.

uninstall.sh

@@ -0,0 +1,32 @@
+#!/usr/bin/env bash
+# Removes this plugin from Nemo. The core, the other plugins and the config
+# file are left alone.
+set -euo pipefail
+
+dataHome="${XDG_DATA_HOME:-$HOME/.local/share}"
+extensionsDir="$dataHome/nemo-python/extensions"
+target="$extensionsDir/nemoRepoEmblems.py"
+
+if [ -e "$target" ]; then
+  rm -f "$target"
+  echo "Removed $target"
+else
+  echo "Not installed: $target"
+fi
+
+rm -f "$extensionsDir/__pycache__/nemoRepoEmblems".*.pyc
+
+iconDir="$dataHome/icons/hicolor/scalable/emblems"
+for name in emblem-repo-git emblem-repo-claude emblem-repo-dirty emblem-repo-unpushed; do
+  if [ -e "$iconDir/$name.svg" ]; then
+    rm -f "$iconDir/$name.svg"
+    echo "Removed $iconDir/$name.svg"
+  fi
+done
+
+if command -v gtk-update-icon-cache >/dev/null 2>&1; then
+  gtk-update-icon-cache -f -t "$dataHome/icons/hicolor" >/dev/null 2>&1 || true
+fi
+
+echo
+echo "Restart Nemo to unload it:  nemo -q"