Add import metadata and config ingest/export endpoints
Complete the five-area journal export/import system by adding support for
import metadata (hash-based dedup) and config (always staged with diff).
- POST /ingest/imports: receives import metadata, deduplicates by content
hash, copies new imports, stages ID collisions
- POST /ingest/config: receives config snapshot, computes categorized
field-by-field diff (identity/preference), always stages with
source_config.json + diff.json, never auto-merges
- sol export --only imports: scans journal/imports/ for metadata dirs,
excludes sync state files (via SYNCABLE_REGISTRY) and source state dirs,
sends delta based on manifest
- sol export --only config: strips never-transfer fields, sends snapshot
- Both areas added to default export sequence (after facets)
- Dry-run, state tracking, and decision logs for both areas