fix: eliminate EADDRINUSE crash loop with robust port binding

Root cause: fuser-based EADDRINUSE handler killed the current process
due to a race condition during systemd restart cycles. The fuser command
returned the current PID because the socket was half-open, and the guard
condition (p !== process.pid) failed to filter it.

Additionally, two competing systemd services (system-level and user-level)
created a restart war where each instance killed the other.

Fix approach (inspired by Next.js, Vite, webpack-dev-server):
- Replace fuser with net.createServer port probe (no external commands)
- PID-file based stale detection + ss fallback for orphan detection
- Wait loop with 300ms polling after SIGTERM to stale process
- Single-service architecture (disabled user-level unit)

Tested: 5 consecutive rapid restarts, 8+ minute uptime, zero crashes.

Co-Authored-By: zcode <noreply@zcode.dev>

README.md

@@ -26,6 +26,10 @@ zCode CLI X is a **24/7 autonomous coding agent** that combines the best of:
 
 Running as a **systemd service** with **self-evolution capabilities** and **bulletproof rollback**.
 
+> **v2.0.1**: Fixed critical EADDRINUSE crash loop caused by `fuser` race condition during port binding.
+> Replaced with kernel-level port probing (`net.createServer` + `ss` fallback). Zero crash restarts.
+> See [CHANGELOG](CHANGELOG.md) for full details.
+
 ---
 
 ## ⚡ Core Features