Create dedicated network collector with physical/virtual interface grouping

Move network collection from NixOS collector to dedicated NetworkCollector. Add link status detection for physical interfaces (up/down). Group interfaces by physical/virtual, show status icons for physical NICs only. Down interfaces show as Inactive instead of Critical.

Version bump to 0.1.165

agent/src/collectors/mod.rs

@@ -7,6 +7,7 @@ pub mod cpu;
 pub mod disk;
 pub mod error;
 pub mod memory;
+pub mod network;
 pub mod nixos;
 pub mod systemd;