Add comprehensive timeouts to all blocking system commands

Fixes random host disconnections caused by blocking operations preventing timely ZMQ packet transmission.

Changes:
- Add run_command_with_timeout() wrapper using tokio for async command execution
- Apply 10s timeout to smartctl (prevents 30+ second hangs on failing drives)
- Apply 5s timeout to du, lsblk, systemctl list commands
- Apply 3s timeout to systemctl show/is-active, df, ip commands
- Apply 2s timeout to hostname command
- Use system 'timeout' command for sync operations where async not needed

Critical fixes:
- smartctl: Failing drives could block for 30+ seconds per drive
- du: Large directories (Docker, PostgreSQL) could block 10-30+ seconds
- systemctl/docker: Commands could block indefinitely during system issues

With 1-second collection interval and 10-second heartbeat timeout, any blocking operation >10s causes false "host offline" alerts. These timeouts ensure collection completes quickly even during system degradation.

agent/src/collectors/network.rs

@@ -51,7 +51,7 @@ impl NetworkCollector {
 
     /// Get the primary physical interface (the one with default route)
     fn get_primary_physical_interface() -> Option<String> {
-        match Command::new("ip").args(["route", "show", "default"]).output() {
+        match Command::new("timeout").args(["2", "ip", "route", "show", "default"]).output() {
             Ok(output) if output.status.success() => {
                 let output_str = String::from_utf8_lossy(&output.stdout);
                 // Parse: "default via 192.168.1.1 dev eno1 ..."
@@ -110,7 +110,7 @@ impl NetworkCollector {
         // Parse VLAN configuration
         let vlan_map = Self::parse_vlan_config();
 
-        match Command::new("ip").args(["-j", "addr"]).output() {
+        match Command::new("timeout").args(["3", "ip", "-j", "addr"]).output() {
             Ok(output) if output.status.success() => {
                 let json_str = String::from_utf8_lossy(&output.stdout);