Fix pulse-host-agent temperature collection on all Linux distros (related to #661)

The temperature collection in pulse-host-agent was broken on all Linux
distributions due to an incorrect platform check.

Root cause:
- collectTemperatures() checked `if a.platform != "linux"` at agent.go:316
- normalisePlatform() returns the raw distro name from gopsutil (debian, ubuntu, pve)
- This caused temperature collection to be skipped on ALL Linux hosts

Fix:
- Changed check to `if runtime.GOOS != "linux"` which correctly identifies Linux
- runtime.GOOS returns "linux" regardless of distribution

Also fixed documentation typo:
- Changed "Servers tab" to "Hosts tab" in HOST_AGENT.md and TEMPERATURE_MONITORING.md
- Reported by user in issue #661 comments

Testing:
- Verified build succeeds
- Confirmed runtime.GOOS returns "linux" on Linux systems

Related to #661

docs/HOST_AGENT.md

@@ -17,7 +17,7 @@ The host agent automatically collects temperature data on Linux systems with lm-
 - **NVMe Drive Temperatures**: SSD thermal data
 - **GPU Temperatures**: AMD and NVIDIA GPU sensors
 
-Temperature data appears in the **Servers** tab alongside other host metrics. This is particularly useful for monitoring Proxmox hosts when running Pulse in a VM (where the sensor proxy socket cannot cross VM boundaries).
+Temperature data appears in the **Hosts** tab alongside other host metrics. This is particularly useful for monitoring Proxmox hosts when running Pulse in a VM (where the sensor proxy socket cannot cross VM boundaries).
 
 **Requirements:**
 - Linux operating system

docs/TEMPERATURE_MONITORING.md

@@ -43,7 +43,7 @@ pulse-host-agent runs natively on your Proxmox host and reports temperatures bac
      bash -s -- --url http://your-pulse-vm:7655 --token YOUR_API_TOKEN
    ```
 
-3. Verify temperatures appear in Pulse UI under the Servers tab
+3. Verify temperatures appear in Pulse UI under the Hosts tab
 
 The host agent will report CPU, NVMe, and GPU temperatures alongside other system metrics. No proxy installation or socket mounting needed.
 

internal/hostagent/agent.go

@@ -313,7 +313,7 @@ func isLoopback(flags []string) bool {
 // Returns an empty Sensors struct if collection fails (best-effort).
 func (a *Agent) collectTemperatures(ctx context.Context) agentshost.Sensors {
 	// Only collect on Linux for now (lm-sensors is Linux-specific)
-	if a.platform != "linux" {
+	if runtime.GOOS != "linux" {
 		return agentshost.Sensors{}
 	}