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/FetchLevel.kt

@@ -14,7 +14,7 @@ internal fun fetchLevel(): Level = level(
     hints = listOf("Look up the 'git fetch' command"),
     commandSuggestions = listOf("git fetch origin"),
     setup = { RepoState(initialized = true, branches = mapOf("master" to 1), remotes = mapOf("origin" to "remote")) },
-    validator = repoPredicate { repo -> "origin/feature_branch" in repo.fetchedBranches && repo.headBranch == "master" },
+    validator = repoPredicate { repo -> "origin/new_branch" in repo.fetchedBranches && repo.headBranch == "master" },
     testCases = listOf(
         levelTestCase("fetch origin", "git fetch origin"),
         levelTestCase("fetch default", "git fetch"),