Auto-start queue when adding jobs from Convert module

Implements automatic queue processing when jobs are added from the Convert
module via the 'Add to Queue' button:

Features:
- IsRunning() method added to queue package to check processing status
- 'Add to Queue' button now auto-starts queue if not already running
- Eliminates need to manually open Queue view and click 'Start Queue'
- Seamless workflow: Add video → Queue → Auto-starts conversion

Before:
1. Load video
2. Click 'Add to Queue'
3. Click 'View Queue'
4. Click 'Start Queue'

After:
1. Load video
2. Click 'Add to Queue' (auto-starts!)
3. Load next video
4. Click 'Add to Queue' (already running)

Perfect for batch operations where user loads multiple videos and expects
them to start encoding immediately.

internal/queue/queue.go

@@ -283,6 +283,13 @@ func (q *Queue) Stop() {
 	q.running = false
 }
 
+// IsRunning returns true if the queue is currently processing jobs
+func (q *Queue) IsRunning() bool {
+	q.mu.RLock()
+	defer q.mu.RUnlock()
+	return q.running
+}
+
 // PauseAll pauses any running job and stops processing
 func (q *Queue) PauseAll() {
 	q.mu.Lock()

main.go

@@ -1880,6 +1880,11 @@ func buildConvertView(state *appState, src *videoSource) fyne.CanvasObject {
 			dialog.ShowError(err, state.window)
 		} else {
 			dialog.ShowInformation("Queue", "Job added to queue!", state.window)
+			// Auto-start queue if not already running
+			if state.jobQueue != nil && !state.jobQueue.IsRunning() {
+				state.jobQueue.Start()
+				logging.Debug(logging.CatUI, "queue auto-started after adding job")
+			}
 		}
 	})
 	if src == nil {