Fix discovery phase appearing frozen

Scanner now updates message every 250 files during os.walk so the UI
shows a live count. Progress bar switches to an indeterminate animated
pulse during discovery and takeout phases (no known total yet), then
reverts to a normal percentage bar once indexing begins.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/scanner.py

@@ -492,6 +492,12 @@ def run_scan(folder_path: str, scan_id: int, mode: str = "incremental"):
                 ext = Path(fname).suffix.lower()
                 if ext in SUPPORTED_EXT:
                     all_files.append(os.path.join(root, fname))
+                    # Live count update every 250 files so UI doesn't look frozen
+                    if len(all_files) % 250 == 0:
+                        scan_state["message"] = f"Discovering... {len(all_files):,} files found"
+
+            if scan_state["cancel_requested"]:
+                break
 
         scan_state["total"] = len(all_files)
         scan_state["message"] = f"Found {len(all_files):,} files"