Server load optimization: spawn_events retention + log spam fix

Database cleanup:
- Converted spawn_events to a TimescaleDB hypertable with 7-day retention.
  Previously a regular table growing unbounded — had reached 482M rows/66GB
  from June 2025. Manual migration copied last 7 days (12M rows) to a new
  hypertable, swapped names, and dropped the old table.
  Result: DB shrunk from 77GB → 12GB.
- Dropped server_health_checks table entirely. It was write-only (850K rows,
  134MB) — only current state in server_status is actually read. Eliminated
  the insert from monitor_server_health().

Telemetry handler cleanup:
- Removed 4 per-message INFO log lines (TELEMETRY_RECEIVED, DB_WRITE_ATTEMPT,
  DB_WRITE_SUCCESS, PROCESSING_COMPLETE). At 60+ chars × every 2s = hundreds
  of log lines/sec. Replaced with single SLOW_* warnings above 500ms/1000ms
  thresholds.
- Removed redundant pool-size introspection (try/except + hasattr) on every
  telemetry message — useless noise in the hot path.
- Removed debug cache-miss and kill-delta logs.

Log level:
- docker-compose.yml: dereth-tracker LOG_LEVEL DEBUG → INFO (was dumping
  entire inventory_delta JSON payloads for every item update).
- inventory-service LOG_LEVEL DEBUG → INFO.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker-compose.yml

@@ -27,9 +27,9 @@ services:
       DB_WAL_AUTOCHECKPOINT_PAGES: "${DB_WAL_AUTOCHECKPOINT_PAGES}"
       SHARED_SECRET: "${SHARED_SECRET}"
       SECRET_KEY: "${SECRET_KEY}"
-      LOG_LEVEL: "DEBUG"
       INVENTORY_SERVICE_URL: "http://inventory-service:8000"
       DISCORD_ACLOG_WEBHOOK: "${DISCORD_ACLOG_WEBHOOK:-}"
+      LOG_LEVEL: "INFO"
     restart: unless-stopped
     logging:
       driver: "json-file"
@@ -72,7 +72,7 @@ services:
       - "./inventory-service:/app"
     environment:
       DATABASE_URL: "postgresql://inventory_user:${INVENTORY_DB_PASSWORD}@inventory-db:5432/inventory_db"
-      LOG_LEVEL: "DEBUG"
+      LOG_LEVEL: "INFO"
     restart: unless-stopped
     logging:
       driver: "json-file"