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/main/java/solutions/tretter/githugandroid/levels/PullLevel.kt

@@ -14,7 +14,11 @@ internal fun pullLevel(): Level = level(
     hints = listOf("Check out the remote repositories and research `git pull`."),
     commandSuggestions = listOf("git pull origin master"),
     setup = { RepoState(initialized = true, remotes = mapOf("origin" to "remote"), branches = mapOf("master" to 1)) },
-    validator = repoPredicate { repo -> "origin/master" in repo.fetchedBranches },
+    validator = repoPredicate { repo ->
+        "origin/master" in repo.fetchedBranches &&
+            repo.files.any { it.name == "remote_file" && it.tracked } &&
+            repo.commits.size >= 2
+    },
     testCases = listOf(
         levelTestCase("pull explicit remote branch", "git pull origin master"),
         levelTestCase("pull default origin", "git pull"),