Add global installation capability and fix venv accessibility issue

- Add make install-global target with intelligent installation methods
- Support pipx (recommended), pip --user, and fallback options
- Resolve issue where kaizen-agentic was only available in local venv
- Update documentation to clearly explain 4 installation options:
  - Development mode (local venv)
  - Global installation (any directory)
  - Local package testing (local venv)
  - Future PyPI installation
- CLI now available globally from any directory after make install-global

Fixes the core issue where users couldn't access kaizen-agentic from other repos.

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

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

README.md

@@ -14,21 +14,32 @@ git clone https://github.com/kaizen-agentic/kaizen-agentic.git
 cd kaizen-agentic
 make setup-complete
 make agents-install-cli
-source .venv/bin/activate
+source .venv/bin/activate  # Required for each session
 ```
 
-**From Local Package (Test Installation):**
+**Global Installation (Available from any directory):**
+```bash
+git clone https://github.com/kaizen-agentic/kaizen-agentic.git
+cd kaizen-agentic
+make setup-complete
+python3 -m build && make install-global
+# No virtual environment activation needed
+```
+
+**Local Package Testing:**
 ```bash
 git clone https://github.com/kaizen-agentic/kaizen-agentic.git
 cd kaizen-agentic
 make setup-complete
 python3 -m build && make install-local
-source .venv/bin/activate
+source .venv/bin/activate  # Required for each session
 ```
 
 **From PyPI (Coming Soon):**
 ```bash
 pip install kaizen-agentic  # Available after v1.0.0 publication
+# or
+pipx install kaizen-agentic  # Recommended for global CLI tools
 ```
 
 ### Your First Project (New Users)