feat: add containerization detection to version endpoint

Added containerized and containerId fields to /api/version endpoint
to enable automatic temperature proxy installation for LXC containers.

Changes:
- Added Containerized bool field to VersionResponse
- Added ContainerId string field to VersionResponse
- Detect containerization by checking /run/systemd/container file
- Extract container ID from hostname for LXC containers
- Set deployment type from container type (lxc/docker)

This allows the PVE setup script to:
1. Detect that Pulse is running in a container
2. Find the container ID by matching IPs
3. Automatically install pulse-sensor-proxy on the host
4. Configure bind mount for secure socket communication

Fixes the issue where setup script showed 'Proxy not available'
even when Pulse was containerized.

internal/api/router.go

@@ -2264,6 +2264,22 @@ func (r *Router) handleVersion(w http.ResponseWriter, req *http.Request) {
 		DeploymentType: versionInfo.DeploymentType,
 	}
 
+	// Detect containerization (LXC/Docker)
+	if containerType, err := os.ReadFile("/run/systemd/container"); err == nil {
+		response.Containerized = true
+
+		// Try to get container ID from hostname (LXC containers often use CTID as hostname)
+		if hostname, err := os.Hostname(); err == nil {
+			// For LXC, try to extract numeric ID from hostname or use full hostname
+			response.ContainerId = hostname
+		}
+
+		// Add container type to deployment type if not already set
+		if response.DeploymentType == "" {
+			response.DeploymentType = string(containerType)
+		}
+	}
+
 	// Add cached update info if available
 	if cachedUpdate := r.updateManager.GetCachedUpdateInfo(); cachedUpdate != nil {
 		response.UpdateAvailable = cachedUpdate.Available

internal/api/types.go

@@ -33,6 +33,8 @@ type VersionResponse struct {
 	DeploymentType  string `json:"deploymentType,omitempty"`
 	UpdateAvailable bool   `json:"updateAvailable"`
 	LatestVersion   string `json:"latestVersion,omitempty"`
+	Containerized   bool   `json:"containerized"`
+	ContainerId     string `json:"containerId,omitempty"`
 }
 
 // ErrorResponse represents an error response