Improve upstream parity for level fixtures

- Add native per-level fixtures for complex histories, tags, branch graphs, rebases, resets, restores, stashes, and local remotes.
- Strengthen repository inspection so branch commit counts, remote-tracking branches, and detached tag checkouts reflect real Git state.
- Align Fetch, Pull, Push Branch, Branch At, and Rebase validators/tests with upstream-style repository state.
- Keep the prompt callout and native filesystem tab-completion fixes from the previous batch.

app/src/test/java/solutions/tretter/githugandroid/GitSandboxEngineTest.kt

@@ -3,7 +3,10 @@ package solutions.tretter.githugandroid
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertFalse
 import org.junit.Assert.assertTrue
+import org.junit.Assume.assumeTrue
 import org.junit.Test
+import java.io.File
+import java.nio.file.Files
 
 class GitSandboxEngineTest {
     @Test
@@ -147,6 +150,31 @@ class GitSandboxEngineTest {
         assertEquals(listOf("model/"), directoryCompletionCandidates(repo))
     }
 
+    @Test
+    fun nativeCompletionUsesCurrentDirectoryIncludingGitMetadata() {
+        val git = File("/usr/bin/git")
+        assumeTrue(git.exists() && git.canExecute())
+        val root = Files.createTempDirectory("githug-completion").toFile()
+        try {
+            val runtime = GitRepositoryRuntime(root, git)
+            val level = level(
+                id = "completion-test",
+                title = "Completion Test",
+                description = "",
+                hints = emptyList(),
+                commandSuggestions = emptyList(),
+                setup = { RepoState(initialized = true) },
+                validator = { _, _ -> false },
+            )
+            val repo = runtime.prepareLevel(level)
+            val (gitDirRepo, _) = runtime.execute(level, repo, "cd .git")
+
+            assertTrue("HEAD" in runtime.completionCandidates(level, gitDirRepo, directoriesOnly = false))
+        } finally {
+            root.deleteRecursively()
+        }
+    }
+
     @Test
     fun cdDotDotShortcutMovesToParentDirectory() {
         val repo = RepoState(initialized = true, currentDir = "src/main")