Clean up existing install before extracting .mpk (#55)

install_mpk() would fail with EEXIST if the destination folder already
existed from a previous (possibly partial) install, or if a dangling
symlink occupied the path (e.g. a dev symlink whose target was removed).

Before extracting, now remove the destination if it is:
- A real directory (via shutil.rmtree)
- A regular file (via os.remove)
- A symlink, including broken ones (via os.remove as a fallback)

This enables clean reinstalls, updates, and recovery from failed
installs.

Co-authored-by: Richard Taylor <RT@MacBookPro.lan>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

internal_filesystem/lib/mpos/content/app_manager.py

@@ -157,6 +157,25 @@ class AppManager:
     @staticmethod
     def install_mpk(temp_zip_path, dest_folder):
         try:
+            # Step 1: Remove any existing (possibly partial) install or symlink
+            try:
+                st = os.stat(dest_folder)
+                if st[0] & 0x4000:  # It's a real directory
+                    import shutil
+                    shutil.rmtree(dest_folder)
+                    print("Removed existing folder:", dest_folder)
+                else:
+                    os.remove(dest_folder)
+                    print("Removed existing file:", dest_folder)
+            except OSError:
+                pass  # Doesn't exist, that's fine
+            # Also remove if it's a symlink (broken or otherwise)
+            try:
+                os.remove(dest_folder)
+                print("Removed symlink:", dest_folder)
+            except OSError:
+                pass  # Not a symlink or already removed
+
             # Step 2: Unzip the file
             print("Unzipping it to:", dest_folder)
             with zipfile.ZipFile(temp_zip_path, "r") as zip_ref: