Refresh native Git helper aliases after app upgrade

- Rebuild the app-private git-exec helper directory when the packaged native Git binary changes.
- Remove stale helper aliases before recreating symlinks/copies.
- Add regression coverage for refreshing cached Git exec aliases across binary changes.

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

@@ -185,6 +185,37 @@ class GitSandboxEngineTest {
         }
     }
 
+    @Test
+    fun nativeGitExecAliasesRefreshWhenBinaryChanges() {
+        val git = testGitBinary()
+        assumeTrue(git.exists() && git.canExecute())
+        val root = Files.createTempDirectory("githug-exec-refresh").toFile()
+        try {
+            val firstGit = File(root, "first-git").also { git.copyTo(it); it.setExecutable(true) }
+            val secondGit = File(root, "second-git").also { git.copyTo(it); it.setExecutable(true) }
+            val level = level(
+                id = "exec-refresh-test",
+                title = "Exec Refresh Test",
+                description = "",
+                hints = emptyList(),
+                commandSuggestions = emptyList(),
+                setup = { RepoState(initialized = true) },
+                validator = { _, _ -> false },
+            )
+
+            GitRepositoryRuntime(root, firstGit).prepareLevel(level)
+            val alias = File(root, "git-exec/git")
+            assertTrue(alias.exists())
+            assertTrue(File(root, "git-exec/.binary-fingerprint").readText().contains(firstGit.absolutePath))
+
+            GitRepositoryRuntime(root, secondGit).prepareLevel(level)
+            assertTrue(alias.exists())
+            assertTrue(File(root, "git-exec/.binary-fingerprint").readText().contains(secondGit.absolutePath))
+        } finally {
+            root.deleteRecursively()
+        }
+    }
+
     @Test
     fun nativePushLevelHasDivergedStatusAndRebasesCleanly() {
         val git = testGitBinary()