fix(importers): plaud sync emits and checkpoints without waiting on transcription
Add `wait_for_processing` kwarg (default True) to `import_one` so PlaudBackend.sync
can return after segment creation instead of blocking on per-segment transcription.
Sync now also persists imports/plaud.json after each successful per-file import,
so partial progress survives the supervisor max_runtime cap. Interactive
`sol import file.opus` keeps end-to-end behavior via the default. granola.py and
obsidian.py are unchanged — their text-import paths don't use _wait_for_segments.
Co-Authored-By: Codex <codex@openai.com>