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

@@ -12,7 +12,6 @@ PluginComponent {
 
     property bool isConnected: false
     property string tailscaleIP: ""
-    property string _pendingToggleAction: ""
     property string currentExitNode: ""
     property var peers: []
     property string cachedClipboardTool: ""
@@ -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: {
@@ -42,11 +46,10 @@ PluginComponent {
 
         onExited: (code, status) => {
             if (code !== 0) {
-                var action = root._pendingToggleAction || (root.isConnected ? "disconnect" : "connect")
+                var action = root.isConnected ? "disconnect" : "connect"
                 var detail = toggleProcess.stderr.text.trim().slice(0, 120)
                 ToastService.showError("tailscalectl", TailscaleLib.errorMessage(action) + (detail ? " — " + detail : ""))
             }
-            root._pendingToggleAction = ""
             statusCheck.running = true
         }
     }
@@ -92,18 +95,16 @@ 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 = ""
@@ -114,14 +115,11 @@ PluginComponent {
     }
 
     function toggleTailscale() {
-        if (toggleProcess.running) return
-        root._pendingToggleAction = root.isConnected ? "disconnect" : "connect"
         toggleProcess.command = TailscaleLib.buildToggleCommand(root.isConnected)
         toggleProcess.running = true
     }
 
     function setExitNode(hostname) {
-        if (exitNodeProcess.running) return
         exitNodeProcess.command = TailscaleLib.makeExitNodeCommand(hostname)
         exitNodeProcess.running = true
     }