- metadata.py: persistent ExifTool session (avoids Perl startup per file),
filters out File:/ExifTool: noise
- scanner now populates observations.meta as JSONB
- size duplicated into observations for self-contained queries and to
strengthen the rescan idempotency check (path + mtime + size)
- README rewritten with state diagram, schema tables, scan/apply workflow
- observations now keyed by (path, mtime) for idempotent rescans
- new index ix_observations_path_mtime
- mama-dev reset: truncate all data, schema kept
- mama-dev stats: overview, breakdowns by source_kind/status/hostname/MIME, largest blobs
