Move the last explorer workflows onto the focused diff

Historical file removal and the staging/custom-patch demos still entered
the old panels even though their line actions already exist in the main
diff. Preserve their prompts, timing, and downstream results while changing
only the interaction surface.

Co-Authored-By: GitHub Copilot <copilot@github.com>

pkg/integration/tests/commit/discard_old_file_changes.go

@@ -131,9 +131,9 @@ var DiscardOldFileChanges = NewIntegrationTest(NewIntegrationTestArgs{
 				Equals("    A file2ToRemove"),
 			).
 			NavigateToLine(Contains("multiLineFile")).
-			PressEnter()
+			Press(keys.Universal.FocusMainView)
 
-		t.Views().PatchBuilding().
+		t.Views().Main().
 			IsFocused().
 			SelectedLine(
 				Contains("+this file has"),

pkg/integration/tests/demo/custom_patch.go

@@ -52,9 +52,9 @@ var CustomPatch = NewIntegrationTest(NewIntegrationTestArgs{
 					IsFocused().
 					NavigateToLine(Contains("users.go")).
 					Wait(1000).
-					PressEnter().
+					Press(keys.Universal.FocusMainView).
 					Tap(func() {
-						t.Views().PatchBuilding().
+						t.Views().Main().
 							IsFocused().
 							NavigateToLine(Contains("TODO")).
 							Wait(500).

pkg/integration/tests/demo/stage_lines.go

@@ -56,9 +56,9 @@ var StageLines = NewIntegrationTest(NewIntegrationTestArgs{
 
 		t.Views().Files().
 			IsFocused().
-			PressEnter()
+			Press(keys.Universal.FocusMainView)
 
-		t.Views().Staging().
+		t.Views().Main().
 			IsFocused().
 			Press(keys.Universal.ToggleRangeSelect).
 			PressFast(keys.Universal.NextItem).