Parallel adaptive discovery walk; fix PyInstaller tracerite data files

- scanner: replace serial DFS with 16-worker priority work-queue, one
  scandir round trip per directory (DirEntry mtimes), per-subtree
  exponential backoff (persisted in scan-state.json v2), leaf candidates
  gated on max(dir, newest video file) mtime so growing downloads and
  lazy NTFS dir mtimes are handled
- spec: collect_data_files('tracerite') so style.css/script.js ship
- guibuild: tolerate non-UTF-8 console when printing status glyphs
- ruff format pass on indexer.py/index_store.py (hook requirement)

scripts/guibuild.py

@@ -239,6 +239,9 @@ def create_zip(version: str) -> Path:
 
 
 def main() -> None:
+    # Windows consoles default to cp1252, which can't encode ✓/✗
+    sys.stdout.reconfigure(errors="replace")
+    sys.stderr.reconfigure(errors="replace")
     try:
         version = read_version()
         print(f"MediaHive version: {version}")