Fix design-vs-implementation gaps found in verification

Critical fixes:
- Wire monitor subsystem to agent startup (was dead code)
- Implement NodeStatus RPC (disk, memory, CPU, runtime version, uptime)
- Deploy respects active=false (sets desired_state=stopped, not always running)

Medium fixes:
- Add Started field to runtime.ContainerInfo, populate from podman inspect
- Populate ComponentInfo.started in status handlers for uptime display
- Add Monitor field to Agent struct for graceful shutdown

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

go.mod

@@ -5,6 +5,7 @@ go 1.25.7
 require (
 	github.com/pelletier/go-toml/v2 v2.3.0
 	github.com/spf13/cobra v1.10.2
+	golang.org/x/sys v0.42.0
 	google.golang.org/grpc v1.79.3
 	google.golang.org/protobuf v1.36.11
 	modernc.org/sqlite v1.47.0
@@ -19,7 +20,6 @@ require (
 	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
 	github.com/spf13/pflag v1.0.9 // indirect
 	golang.org/x/net v0.48.0 // indirect
-	golang.org/x/sys v0.42.0 // indirect
 	golang.org/x/text v0.32.0 // indirect
 	google.golang.org/genproto/googleapis/rpc v0.0.0-20251202230838-ff82c1b0f217 // indirect
 	modernc.org/libc v1.70.0 // indirect