Fix mcp ps uptime: parse StartedAt from podman ps JSON

List() was not extracting the StartedAt field from podman's JSON
output, so LiveCheck always returned zero timestamps and the CLI
showed "-" for every container's uptime.

podman ps --format json includes StartedAt as a Unix timestamp
(int64). Parse it into ContainerInfo.Started so the existing
LiveCheck → CLI uptime display chain works.

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

internal/runtime/podman.go

@@ -219,6 +219,7 @@ type podmanPSEntry struct {
 	Image     string   `json:"Image"`
 	State     string   `json:"State"`
 	Command   []string `json:"Command"`
+	StartedAt int64    `json:"StartedAt"`
 }
 
 // List returns information about all containers.
@@ -240,12 +241,16 @@ func (p *Podman) List(ctx context.Context) ([]ContainerInfo, error) {
 		if len(e.Names) > 0 {
 			name = e.Names[0]
 		}
-		infos = append(infos, ContainerInfo{
+		info := ContainerInfo{
 			Name:    name,
 			Image:   e.Image,
 			State:   e.State,
 			Version: ExtractVersion(e.Image),
-		})
+		}
+		if e.StartedAt > 0 {
+			info.Started = time.Unix(e.StartedAt, 0)
+		}
+		infos = append(infos, info)
 	}
 
 	return infos, nil