Investigate ev_stations pipeline gap (data/ev-charging.json → Postgres)

Found during 2026-05-25 reflection. scripts/sync-ev-charging.ts writes data/ev-charging.json (40 MB, 87,959 stations as of 2026-05-25 21:53 UTC) but does NOT write to the ev_stations table. Only scripts/seed-database.ts populates ev_stations, and seed has not been run since 2026-04-15, so prod Postgres ev_stations is 41+ days behind the JSON snapshot. Tasks: (1) confirm whether prod app reads from Postgres or from JSON; (2) if Postgres, decide between (a) running seed-database.ts on each sync, (b) adding an incremental upsert step to sync-ev-charging.ts, or (c) a periodic seed-database invocation; (3) ship the chosen fix; (4) document in DB-SCHEMA.md. Same gap likely exists for other JSON sync scripts (power-plants, transmission-lines, pricing-nodes) — audit those too.