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>

internal/runtime/podman.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"os/exec"
 	"strings"
+	"time"
 )
 
 // Podman implements the Runtime interface using the podman CLI.
@@ -98,7 +99,8 @@ type podmanInspectResult struct {
 		User  string   `json:"User"`
 	} `json:"Config"`
 	State struct {
-		Status string `json:"Status"`
+		Status    string `json:"Status"`
+		StartedAt string `json:"StartedAt"`
 	} `json:"State"`
 	HostConfig struct {
 		RestartPolicy struct {
@@ -142,6 +144,9 @@ func (p *Podman) Inspect(ctx context.Context, name string) (ContainerInfo, error
 		Cmd:     r.Config.Cmd,
 		Version: ExtractVersion(r.Config.Image),
 	}
+	if t, err := time.Parse(time.RFC3339Nano, r.State.StartedAt); err == nil {
+		info.Started = t
+	}
 
 	info.Network = r.HostConfig.NetworkMode
 	if len(r.NetworkSettings.Networks) > 0 {