Fix Git editor reword workflow and UI coverage

- show Git editor file paths instead of the submitted git command
- surface follow-up commit message editors during interactive rebase reword
- add rename-commit UI tests for editor and amend-message solution paths
- add broader embedded level solution scenarios for alternate Git workflows

app/src/main/java/solutions/tretter/githugandroid/levels/AddLevel.kt

@@ -18,5 +18,7 @@ internal fun addLevel(): Level = level(
     testCases = listOf(
         levelTestCase("add exact file", "git add README"),
         levelTestCase("add all", "git add ."),
+        levelTestCase("stage exact file", "git stage README"),
+        levelTestCase("add with path separator", "git add -- README"),
     ),
 )