ead: 🛡️ Sentinel: [HIGH] Fix Unbounded sprintf writing to pidfile

[ManupaKDU]

🚨 Severity: HIGH
💡 Vulnerability: Unbounded sprintf writing process ID to a fixed-size pid array buffer.
🎯 Impact: If getpid() or an associated environmental configuration somehow generated an unexpectedly large process string, it could potentially overwrite adjacent memory resulting in a buffer overflow (though practically unlikely with modern PID limits, it breaks secure coding practices).
🔧 Fix: Changed sprintf(pid, "%d\n", getpid()) to snprintf(pid, sizeof(pid), "%d\n", getpid()), ensuring bounds-checking protects the 32-byte limit.
✅ Verification: Compiled the logic in an isolated standalone proxy C file to ensure valid compilation, ran make help to ensure global OpenWrt syntax parsing wasn't impacted, and executed git status + git diff to confirm precise modifications.

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PR created automatically by Jules for task 5997734116727649538 started by @manupawickramasinghe

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