Fix all flake8 violations across the codebase

CODE STYLE FIXES:
- Fixed line length violations by breaking long lines appropriately
- Removed unused imports (os from installer.py and registry.py)
- Removed unused variables (package_name in _create_pyproject_toml)
- Fixed f-string usage (removed f-strings without placeholders)
- Fixed import organization and removed redundant imports
- Added missing newlines at end of files

SPECIFIC FIXES:
- cli.py: Split long option line, fixed f-string usage, added newline
- installer.py: Removed unused imports/variables, fixed line breaks, improved validation logic
- registry.py: Removed unused import/variable, broke long condition line
- test files: Removed unused imports, fixed long assertion lines, added newlines

All 24 tests still pass and flake8 now reports no violations.
Code is now compliant with PEP 8 style guidelines.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/kaizen_agentic/cli.py

@@ -17,7 +17,9 @@ def cli():
 
 
 @cli.command()
-@click.option('--category', type=click.Choice([c.value for c in AgentCategory]), help='Filter by category')
+@click.option('--category',
+              type=click.Choice([c.value for c in AgentCategory]),
+              help='Filter by category')
 @click.option('--verbose', '-v', is_flag=True, help='Show detailed information')
 def list(category: Optional[str], verbose: bool):
     """List available agents."""
@@ -195,10 +197,10 @@ def init(project_name: str, template: str, agents: Optional[str], parent_dir: st
     success_count = sum(1 for status in results.values() if status == "INSTALLED")
     click.echo(f"\nProject initialized with {success_count}/{len(results)} agents")
 
-    click.echo(f"\nNext steps:")
+    click.echo("\nNext steps:")
     click.echo(f"  cd {project_name}")
-    click.echo(f"  make setup-complete  # Set up development environment")
-    click.echo(f"  make test           # Run tests")
+    click.echo("  make setup-complete  # Set up development environment")
+    click.echo("  make test           # Run tests")
 
 
 @cli.command()
@@ -308,7 +310,7 @@ def status(target: str):
         click.echo("❌ No agents installed")
 
     # Check for configuration files
-    click.echo(f"\nConfiguration files:")
+    click.echo("\nConfiguration files:")
     config_files = ["CLAUDE.md", "Makefile", "pyproject.toml", ".gitignore"]
     for config_file in config_files:
         file_path = target_path / config_file
@@ -351,4 +353,4 @@ def _get_registry() -> AgentRegistry:
 
 
 if __name__ == '__main__':
-    cli()
+    cli()