feat: add systemd user services and timer units

- Create systemd user service files for both Go and Rust implementations
- Add comprehensive timer configurations: 30-minute, hourly, and daily schedules
- Include security settings, resource limits, and proper service dependencies
- Add justfile recipes for service management (install, enable, disable, status)
- Remove deprecated Makefile in favor of just-based build system
- Fix Rust compilation warnings in imap.rs

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

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

justfile

@@ -135,4 +135,95 @@ versions: build
     @./rust/target/release/mail2couch-rs --version
 
 # Clean and rebuild everything
-rebuild: clean build
+rebuild: clean build
+
+# Systemd service management
+
+# Install systemd user service files
+install-services:
+    @echo "Installing systemd user service files..."
+    mkdir -p ~/.config/systemd/user
+    cp systemd/*.service ~/.config/systemd/user/
+    cp systemd/*.timer ~/.config/systemd/user/
+    systemctl --user daemon-reload
+    @echo "✅ Installed systemd user services and timers"
+    @echo "💡 Enable with: systemctl --user enable mail2couch-{go,rs}.service"
+    @echo "💡 Enable timers with: systemctl --user enable mail2couch-{go,rs}.timer"
+
+# Uninstall systemd user service files
+uninstall-services:
+    @echo "Uninstalling systemd user service files..."
+    systemctl --user stop mail2couch-go.service mail2couch-rs.service || true
+    systemctl --user stop mail2couch-go.timer mail2couch-rs.timer || true
+    systemctl --user stop mail2couch-go-hourly.timer mail2couch-rs-hourly.timer || true
+    systemctl --user stop mail2couch-go-daily.timer mail2couch-rs-daily.timer || true
+    systemctl --user disable mail2couch-go.service mail2couch-rs.service || true
+    systemctl --user disable mail2couch-go.timer mail2couch-rs.timer || true
+    systemctl --user disable mail2couch-go-hourly.timer mail2couch-rs-hourly.timer || true
+    systemctl --user disable mail2couch-go-daily.timer mail2couch-rs-daily.timer || true
+    rm -f ~/.config/systemd/user/mail2couch-*.service
+    rm -f ~/.config/systemd/user/mail2couch-*.timer
+    systemctl --user daemon-reload
+    @echo "✅ Uninstalled systemd user services and timers"
+
+# Show systemd service status
+service-status:
+    @echo "Service status:"
+    systemctl --user status mail2couch-go.service || true
+    systemctl --user status mail2couch-rs.service || true
+    @echo ""
+    @echo "Timer status:"
+    systemctl --user list-timers mail2couch-*
+
+# Enable Go implementation with default 30-minute timer
+enable-go:
+    systemctl --user enable mail2couch-go.service
+    systemctl --user enable mail2couch-go.timer
+    systemctl --user start mail2couch-go.timer
+    @echo "✅ Enabled Go implementation with 30-minute timer"
+
+# Enable Rust implementation with default 30-minute timer
+enable-rust:
+    systemctl --user enable mail2couch-rs.service
+    systemctl --user enable mail2couch-rs.timer
+    systemctl --user start mail2couch-rs.timer
+    @echo "✅ Enabled Rust implementation with 30-minute timer"
+
+# Enable Go implementation with hourly timer
+enable-go-hourly:
+    systemctl --user enable mail2couch-go.service
+    systemctl --user enable mail2couch-go-hourly.timer
+    systemctl --user start mail2couch-go-hourly.timer
+    @echo "✅ Enabled Go implementation with hourly timer"
+
+# Enable Rust implementation with hourly timer
+enable-rust-hourly:
+    systemctl --user enable mail2couch-rs.service
+    systemctl --user enable mail2couch-rs-hourly.timer
+    systemctl --user start mail2couch-rs-hourly.timer
+    @echo "✅ Enabled Rust implementation with hourly timer"
+
+# Enable Go implementation with daily timer
+enable-go-daily:
+    systemctl --user enable mail2couch-go.service
+    systemctl --user enable mail2couch-go-daily.timer
+    systemctl --user start mail2couch-go-daily.timer
+    @echo "✅ Enabled Go implementation with daily timer"
+
+# Enable Rust implementation with daily timer
+enable-rust-daily:
+    systemctl --user enable mail2couch-rs.service
+    systemctl --user enable mail2couch-rs-daily.timer
+    systemctl --user start mail2couch-rs-daily.timer
+    @echo "✅ Enabled Rust implementation with daily timer"
+
+# Disable all timers and services
+disable-all:
+    systemctl --user stop mail2couch-go.timer mail2couch-rs.timer || true
+    systemctl --user stop mail2couch-go-hourly.timer mail2couch-rs-hourly.timer || true
+    systemctl --user stop mail2couch-go-daily.timer mail2couch-rs-daily.timer || true
+    systemctl --user disable mail2couch-go.timer mail2couch-rs.timer || true
+    systemctl --user disable mail2couch-go-hourly.timer mail2couch-rs-hourly.timer || true
+    systemctl --user disable mail2couch-go-daily.timer mail2couch-rs-daily.timer || true
+    systemctl --user disable mail2couch-go.service mail2couch-rs.service || true
+    @echo "✅ Disabled all timers and services"