[events] Wire into ingestion pipeline #664

Replace the existing EventWriter.InsertEvents() in the ingestion service with the hot segment write path. This is the integration point:

• Extract events from LedgerCloseMeta (reuse existing extraction logic)
• Write to hot segment
• Trigger freeze when segment reaches 10,000 ledgers
• Replace event query path with query router

Integration tests required:

• Ingest enough ledgers to fill a segment → verify freeze triggers → verify cold segment is queryable
• Query across hot + cold segments
• Restart after ingestion → verify recovery → continue ingesting