enhance: Add comprehensive .gitignore for deb-mock project

- Add mock-specific build artifacts (chroot/, mock-*, mockroot/)
- Include package build files (*.deb, *.changes, *.buildinfo)
- Add development tools (.coverage, .pytest_cache, .tox)
- Include system files (.DS_Store, Thumbs.db, ._*)
- Add temporary and backup files (*.tmp, *.bak, *.backup)
- Include local configuration overrides (config.local.yaml, .env.local)
- Add test artifacts and documentation builds
- Comprehensive coverage for Python build system project

This ensures build artifacts, chroot environments, and development
tools are properly ignored in version control.

docs/script/validate-html

@@ -0,0 +1,28 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+require "w3c_validators"
+
+def validator(file)
+  extension = File.extname(file)
+  if extension == ".html"
+    W3CValidators::NuValidator.new
+  elsif extension == ".css"
+    W3CValidators::CSSValidator.new
+  end
+end
+
+def validate(file)
+  puts "Checking #{file}..."
+
+  path = File.expand_path "../_site/#{file}", __dir__
+  results = validator(file).validate_file(path)
+
+  return puts "Valid!" if results.errors.empty?
+
+  results.errors.each { |err| puts err.to_s }
+  exit 1
+end
+
+validate "index.html"
+validate File.join "assets", "css", "style.css"