feat: implement just-based build system with distinct binary names

Replace Makefile with justfile for better build management:

Build System Changes:
- Add comprehensive justfile with recipes for both implementations
- Configure Go to build as `mail2couch-go`
- Configure Rust to build as `mail2couch-rs` via Cargo.toml
- Add universal build, test, clean, and install recipes
- Include development convenience recipes and utility commands

New Justfile Features:
- `just build` - builds both implementations
- `just install` - installs both to /usr/local/bin
- `just test` - runs tests for both implementations
- `just sizes` - shows binary size comparison
- `just versions` - compares version outputs
- `just --list` - shows all available recipes

Documentation Updates:
- Update CLAUDE.md with justfile usage examples
- Replace make commands with just equivalents
- Add new utility commands (sizes, versions)
- Update IMPLEMENTATION_COMPARISON.md deployment sections

Benefits of just over make:
- Better command-line interface with `--list`
- More intuitive recipe syntax
- Better suited for development workflows
- Cross-platform compatibility
- Built-in help and documentation

Binary Naming:
- Go implementation: `mail2couch-go` (11M)
- Rust implementation: `mail2couch-rs` (8.3M)
- Clear distinction prevents conflicts
- Parallel installation support

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

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

IMPLEMENTATION_COMPARISON.md

@@ -442,6 +442,8 @@ Both implementations currently share the same security limitations and features:
 
 ### Go Implementation Deployment
 
+**Binary Name**: `mail2couch-go`
+
 **Advantages**:
 - Single binary deployment
 - Minimal system dependencies
@@ -450,16 +452,21 @@ Both implementations currently share the same security limitations and features:
 
 **Best Practices**:
 ```bash
-# Build for production
-cd go && go build -ldflags="-s -w" -o mail2couch .
+# Build for production using justfile
+just build-go-release
+
+# Or build directly
+cd go && go build -ldflags="-s -w" -o mail2couch-go .
 
 # Deploy with systemd service
-sudo cp mail2couch /usr/local/bin/
-sudo systemctl enable mail2couch.service
+sudo cp go/mail2couch-go /usr/local/bin/
+sudo systemctl enable mail2couch-go.service
 ```
 
 ### Rust Implementation Deployment
 
+**Binary Name**: `mail2couch-rs`
+
 **Advantages**:
 - Better resource utilization under load
 - Superior error recovery
@@ -468,18 +475,33 @@ sudo systemctl enable mail2couch.service
 
 **Best Practices**:
 ```bash
-# Build optimized release
+# Build optimized release using justfile
+just build-rust-release
+
+# Or build directly
 cd rust && cargo build --release
 
 # Deploy with enhanced monitoring
-sudo cp target/release/mail2couch /usr/local/bin/
-sudo systemctl enable mail2couch.service
+sudo cp rust/target/release/mail2couch-rs /usr/local/bin/
+sudo systemctl enable mail2couch-rs.service
 
 # Configure structured logging
 export RUST_LOG=info
 export MAIL2COUCH_LOG_FORMAT=json
 ```
 
+### Universal Installation
+
+```bash
+# Build and install both implementations
+just build-release
+sudo just install
+
+# This installs:
+# - /usr/local/bin/mail2couch-go
+# - /usr/local/bin/mail2couch-rs
+```
+
 ---
 
 ## Future Development Roadmap