feat: improve installation system with user-local and system-wide options

Update justfile installation system to provide better user experience:

Installation Improvements:
- `just install` - installs to ~/bin (user-local, no sudo required)
- `just system-install` - installs to /usr/local/bin (system-wide, requires sudo)
- `just uninstall` - removes from ~/bin
- `just system-uninstall` - removes from /usr/local/bin (requires sudo)

Benefits:
- User-local installation by default (follows Unix best practices)
- No sudo required for personal installations
- Clear separation between user and system installs
- Easy uninstallation for both scenarios
- Helpful PATH reminder for ~/bin installation

Documentation Updates:
- Update CLAUDE.md with new installation commands
- Update IMPLEMENTATION_COMPARISON.md deployment examples
- Include uninstall instructions for both methods

This follows modern software distribution practices where user-local
installation is preferred for development tools, with system-wide
installation available when needed for shared environments.

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

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

CLAUDE.md

@@ -23,8 +23,17 @@ just build-rust    # Builds rust/target/release/mail2couch-rs
 # Build optimized release versions
 just build-release
 
-# Install both binaries to /usr/local/bin
-sudo just install
+# Install both binaries to ~/bin (user-local)
+just install
+
+# Install both binaries to /usr/local/bin (system-wide)
+sudo just system-install
+
+# Uninstall from ~/bin
+just uninstall
+
+# Uninstall from /usr/local/bin
+sudo just system-uninstall
 
 # Run tests for both implementations
 just test