sync: Update sync scripts to use write API

[victorquinn]

Summary

Update all sync scripts to write to the database via the API instead of committing JSON files to the repo. Add streaming GeoJSON export for tile pipeline.

Scripts to Update

• scripts/sync-ev-charging.ts → use bulk API
• scripts/sync-power-plants.ts → use bulk API
• scripts/sync-power-plants-monthly.ts → use bulk API
• scripts/sync-transmission-lines.ts → use bulk API
• scripts/sync-pricing-nodes.ts → use bulk API
• scripts/sync-ba.ts → use bulk API

New Scripts

• scripts/export-geojson.ts — Streaming batched PostGIS → GeoJSON export
• Trigger cache revalidation after sync via revalidateTag()
• Trigger async tile rebuild via GitHub Actions dispatch

Implementation

• Each sync uses idempotency key: {source}-sync-{date}
• Sync checks feature flag — if 'json', writes to files; if 'database', writes to API
• Streaming GeoJSON export in 1000-record batches (prevents OOM for 85K EV stations)

Acceptance Criteria

• All sync scripts updated with dual-mode support
• Idempotency keys prevent duplicate writes on retry
• Cache revalidation triggered after successful sync
• Streaming GeoJSON export works for all entity types
• npm run build passes

Spec ref: Section 7
Blocked by: #21 (write API)
Blocks: Nothing (but enables full database operation)