Package pkgmgr with multi-format manifests

- Add pyproject.toml and setuptools config for pkgmgr packaging
- Add Nix flake (devShell + pkgmgr package output)
- Add Arch PKGBUILD for system packaging
- Introduce pkgmgr.yml manifest for repo-level dependencies
- Refactor CLI into pkgmgr/cli.py and make main.py a thin entrypoint
- Extend install_repos to handle pkgmgr.yml, PKGBUILD, flake.nix, Ansible and Python manifests
- Enhance status/update to show Nix/yay system status and upgrades
- Improve .gitignore and document requirements.yml

Created with AI (ChatGPT) – see conversation: https://chatgpt.com/share/6932f2ca-f560-800f-8bb0-52cb82f27e88

pyproject.toml

@@ -0,0 +1,35 @@
+[build-system]
+# This tells pip/build how to build your project (PEP 517).
+requires = ["setuptools>=77", "wheel"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "package-manager"
+version = "0.1.0"
+description = "Kevin's Package Manager is a configurable Python tool to manage multiple repositories via Bash."
+readme = "README.md"
+requires-python = ">=3.10"
+
+# Use a simple SPDX license string to avoid the deprecation warning.
+license = "MIT"
+
+authors = [
+  { name = "Kevin Veen-Birkenbach", email = "info@veen.world" }
+]
+
+# Python runtime dependencies.
+dependencies = [
+  "PyYAML"
+]
+
+[project.urls]
+Homepage = "https://www.veen.world"
+Repository = "https://github.com/kevinveenbirkenbach/package-manager"
+Funding-GitHub-Sponsors = "https://github.com/sponsors/kevinveenbirkenbach"
+Funding-Patreon = "https://www.patreon.com/c/kevinveenbirkenbach"
+Funding-BuyMeACoffee = "https://buymeacoffee.com/kevinveenbirkenbach"
+Funding-PayPal = "https://s.veen.world/paypaldonate"
+
+[tool.setuptools]
+packages = ["pkgmgr"]
+