Refactor think/importer.py into think/importers/ package
Split monolithic importer module into focused submodules:
- cli.py: CLI entry point and Callosum status tracking
- audio.py: audio segmentation (slice, duration, prepare)
- text.py: transcript processing and PDF reading
- shared.py: cross-cutting helpers (JSONL writing, import setup, summary)
- utils.py: journal-side import utilities (moved from think/importer_utils.py)
- plaud.py: Plaud API sync (relocated from observe/plaud.py)
Updated all callers: sol.py, apps/import/routes.py, tests, docs.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>