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>

justfile

@@ -31,14 +31,39 @@ build-go-release:
 # Build optimized Rust release (already built with --release above)
 build-rust-release: build-rust
 
-# Install binaries to /usr/local/bin (requires sudo)
+# Install binaries to ~/bin (user-local installation)
 install: build-release
+    @echo "Installing binaries to ~/bin..."
+    mkdir -p ~/bin
+    cp go/mail2couch-go ~/bin/
+    cp rust/target/release/mail2couch-rs ~/bin/
+    chmod +x ~/bin/mail2couch-go
+    chmod +x ~/bin/mail2couch-rs
+    @echo "✅ Installed mail2couch-go and mail2couch-rs to ~/bin"
+    @echo "💡 Make sure ~/bin is in your PATH"
+
+# Install binaries to /usr/local/bin (system-wide installation, requires sudo)
+system-install: build-release
     @echo "Installing binaries to /usr/local/bin..."
     sudo cp go/mail2couch-go /usr/local/bin/
     sudo cp rust/target/release/mail2couch-rs /usr/local/bin/
     sudo chmod +x /usr/local/bin/mail2couch-go
     sudo chmod +x /usr/local/bin/mail2couch-rs
-    @echo "✅ Installed mail2couch-go and mail2couch-rs"
+    @echo "✅ Installed mail2couch-go and mail2couch-rs to /usr/local/bin"
+
+# Uninstall binaries from ~/bin
+uninstall:
+    @echo "Uninstalling binaries from ~/bin..."
+    rm -f ~/bin/mail2couch-go
+    rm -f ~/bin/mail2couch-rs
+    @echo "✅ Uninstalled mail2couch-go and mail2couch-rs from ~/bin"
+
+# Uninstall binaries from /usr/local/bin (requires sudo)
+system-uninstall:
+    @echo "Uninstalling binaries from /usr/local/bin..."
+    sudo rm -f /usr/local/bin/mail2couch-go
+    sudo rm -f /usr/local/bin/mail2couch-rs
+    @echo "✅ Uninstalled mail2couch-go and mail2couch-rs from /usr/local/bin"
 
 # Run tests for both implementations
 test: test-go test-rust