fix: remove binaryAvailable, fix statusCheck parser location, add timer guard

- Revert binaryAvailable property: reintroduced stale-state anti-pattern
  already rejected in #11. All error paths already handled by Process
  onExited handlers.
- Move statusCheck parsing from onStreamFinished to onExited (#38):
  parser now only runs after exit code validation, preventing stale
  data from being applied on failure.
- Add refreshTimer guard (#44): timer no longer spawns new statusCheck
  while one is already running.

Closes #38, #44. Reverts #52 partial fix.

tailscalectl/TailscaleWidget.qml

@@ -11,7 +11,6 @@ PluginComponent {
     id: root
 
     property bool isConnected: false
-    property bool binaryAvailable: true
     property string tailscaleIP: ""
     property string currentExitNode: ""
     property var peers: []
@@ -25,10 +24,15 @@ PluginComponent {
     popoutHeight: 400
 
     Timer {
+        id: refreshTimer
         interval: 5000
         running: true
         repeat: true
-        onTriggered: statusCheck.running = true
+        onTriggered: {
+            if (!statusCheck.running) {
+                statusCheck.running = true
+            }
+        }
     }
 
     Component.onCompleted: {
@@ -91,46 +95,31 @@ PluginComponent {
 
         command: ["tailscale", "status", "--json"]
 
-        stdout: StdioCollector {
-            onStreamFinished: {
-                const state = TailscaleLib.parseStatusResult(this.text)
+        stdout: StdioCollector {}
+
+        onExited: (code, status) => {
+            if (code === 0) {
+                const state = TailscaleLib.parseStatusResult(statusCheck.stdout.text)
                 root.isConnected = state.isConnected
                 root.tailscaleIP = state.tailscaleIP
                 root.currentExitNode = state.currentExitNode
                 root.peers = state.peers
-            }
-        }
-
-        onExited: (code, status) => {
-            if (code !== 0) {
+            } else {
                 root.isConnected = false
                 root.tailscaleIP = ""
                 root.currentExitNode = ""
                 root.peers = []
-                if (code === 127) {
-                    root.binaryAvailable = false
-                    ToastService.showError("tailscalectl", "Tailscale binary not found")
-                } else {
                 ToastService.showError("tailscalectl", TailscaleLib.errorMessage("status"))
             }
         }
     }
-    }
 
     function toggleTailscale() {
-        if (!root.binaryAvailable) {
-            ToastService.showError("tailscalectl", "Tailscale not available")
-            return
-        }
         toggleProcess.command = TailscaleLib.buildToggleCommand(root.isConnected)
         toggleProcess.running = true
     }
 
     function setExitNode(hostname) {
-        if (!root.binaryAvailable) {
-            ToastService.showError("tailscalectl", "Tailscale not available")
-            return
-        }
         exitNodeProcess.command = TailscaleLib.makeExitNodeCommand(hostname)
         exitNodeProcess.running = true
     }
@@ -167,14 +156,6 @@ PluginComponent {
                 width: parent.width
                 height: Theme.spacingM + statusRow.implicitHeight + Theme.spacingM + peerList.height + Theme.spacingM
 
-                StyledText {
-                    visible: !root.binaryAvailable
-                    text: "Tailscale not available"
-                    anchors.centerIn: parent
-                    font.pixelSize: Theme.fontSizeSmall
-                    color: Theme.surfaceVariantText
-                }
-
                 Row {
                     id: statusRow
                     y: Theme.spacingM