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.

pyproject.toml

@@ -0,0 +1,27 @@
+[build-system]
+requires = ["setuptools>=61"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "nemo-repo-core"
+version = "1.0.0"
+description = "Shared foundation for repository-aware Nemo file manager plugins"
+readme = "README.md"
+requires-python = ">=3.8"
+license = { text = "MIT" }
+authors = [{ name = "DualFroz" }]
+keywords = ["nemo", "cinnamon", "git", "file-manager", "nemo-python"]
+classifiers = [
+  "Environment :: X11 Applications :: GTK",
+  "Intended Audience :: Developers",
+  "License :: OSI Approved :: MIT License",
+  "Operating System :: POSIX :: Linux",
+  "Programming Language :: Python :: 3",
+  "Topic :: Desktop Environment :: File Managers",
+]
+
+[project.urls]
+Homepage = "https://github.com/dualfroz/nemo-repo-core"
+
+[tool.setuptools]
+packages = ["nemoRepoCore"]