feat: add process management commands for daemon control

Add systemd-style subcommands for managing KVS instances:
- start <config>  - Daemonize and run in background
- stop <config>   - Gracefully stop daemon
- restart <config> - Restart daemon
- status [config] - Show status of all or specific instances

Key features:
- PID files stored in ~/.kvs/pids/ (global across all directories)
- Logs stored in ~/.kvs/logs/
- Config names support both 'node1' and 'node1.yaml' formats
- Backward compatible: 'kvs config.yaml' still runs in foreground
- Proper stale PID detection and cleanup

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

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

.gitignore

@@ -1,4 +1,5 @@
 .claude/
+.kvs/
 data/
 data*/
 *.yaml