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>

tests/test_installer.py

@@ -1,7 +1,7 @@
 """Tests for agent installer functionality."""
 
-import pytest
 import json
+import pytest
 from pathlib import Path
 from kaizen_agentic.installer import AgentInstaller, ProjectInitializer, InstallationConfig
 from kaizen_agentic.registry import AgentRegistry
@@ -192,7 +192,7 @@ def test_project_initializer(test_registry, tmp_path):
     initializer = ProjectInitializer(test_registry)
     project_dir = tmp_path / "new_project"
 
-    results = initializer.init_project(
+    initializer.init_project(
         project_dir,
         template="python-basic",
         project_name="new_project"
@@ -217,7 +217,7 @@ def test_project_initializer_custom_agents(test_registry, tmp_path):
     initializer = ProjectInitializer(test_registry)
     project_dir = tmp_path / "custom_project"
 
-    results = initializer.init_project(
+    initializer.init_project(
         project_dir,
         template="python-basic",
         agent_names=["base-agent", "todo-keeper"],
@@ -243,4 +243,4 @@ def test_installation_config():
     assert config.claude_config_path == Path("/tmp/test/claude.json")
     assert config.makefile_path == Path("/tmp/test/Makefile")
     assert config.update_docs is True
-    assert config.create_backup is False
+    assert config.create_backup is False