Import FMG full-JSON export (cultures, religions, states, provinces, regiments)

[barrulus]

Current state

We import individual GeoJSON files via per-layer ingestors:

1. Cells — ingest_cells()
2. Burgs — ingest_burgs()
3. Routes — ingest_routes()
4. Rivers — ingest_rivers()
5. Markers — ingest_markers()

Cultures, religions, states, provinces, and regiments are missing.

Proposal

Rather than building five more per-layer GeoJSON ingestors, switch to consuming FMG's full-JSON export in one pass. FMG can export the entire world model — cells, burgs, routes, rivers, markers, cultures, religions, states, provinces, regiments, military, biomes, etc. — as a single JSON document. One ingestor that walks the FMG export and fans out into the relevant tables avoids the format drift we've been hitting between the per-layer GeoJSONs and the FMG source data.

Scope

• Reuse / consolidate the existing per-layer ingest logic where possible (cells/burgs/routes/rivers/markers).
• Add new ingest paths for cultures, religions, states, provinces, regiments.
• Single command / API entrypoint that takes the FMG full-JSON file.
• Per-layer skip flags so a re-import doesn't have to redo cells from scratch.

Out of scope

• Anything that requires running FMG itself; we consume the exported file.
• Live FMG ↔ Questables sync.

[barrulus]

I want to revisit this with the new FMG export to JSON as a possible extract/import in a single pass for all data.