Extract showUpscaleView and AI helper functions to upscale_module.go

- Move showUpscaleView() from main.go to upscale_module.go
- Remove AI helper functions (detectAIUpscaleBackend, checkAIFaceEnhanceAvailable, etc.)
- Syntax passes, ready for further migration
- Build error is unrelated Fyne API issue in internal/ui

main.go

@@ -2784,13 +2784,6 @@ func (s *appState) showPlayerView() {
 	s.setContent(buildPlayerView(s))
 }
 
-func (s *appState) showUpscaleView() {
-	s.stopPreview()
-	s.lastModule = s.active
-	s.active = "upscale"
-	s.setContent(buildUpscaleView(s))
-}
-
 func (s *appState) showAuthorView() {
 	s.stopPreview()
 	s.lastModule = s.active

upscale_module.go

@@ -170,4 +170,11 @@ func sanitizeForPath(label string) string {
 	return strings.ToLower(r.Replace(label))
 }
 
-// Main module functions will be added here incrementally...
+func (s *appState) showUpscaleView() {
+	s.stopPreview()
+	s.lastModule = s.active
+	s.active = "upscale"
+	s.setContent(buildUpscaleView(s))
+}
+
+// buildUpscaleView and executeUpscaleJob will be added here incrementally...