v0.5.0

Highlights (full notes: docs/CHANGELOG.md → 0.5.0):

• Per-file on_result hook on the upload/sync batch helpers (provenance/logging).
• Default (connect, read) timeouts on control-plane calls — fail fast instead of
  hanging; generate_index(wait=True) tolerates + diagnoses transient poll timeouts.
• New "Extensions" docs section + "ARCANA incremental sync" how-to.