feat(go-services): tracker share_* handlers (complete ingest) + shadow tuning

- share.go: cross-machine vital sharing (share_subscribe/unsubscribe/share_*),
  faithful port of the peer-state snapshot + plugin fan-out + /vital-sharing/peers.
  The last ingest handler — the Go tracker now handles every plugin event type.
- shadow consumer: drop the outbound keepalive ping (the firehose is never idle)
  and tighten the read-deadline watchdog to 12s for faster reconnect after the
  upstream's periodic eviction (full-firehose browser clients get evicted ~every
  90s; the watchdog recovers it, ~90% duty cycle). Production-bound /ws/position
  is unaffected (plugins connect to us; no eviction).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

go-services/tracker-go/main.go

@@ -116,7 +116,7 @@ func main() {
 				logger.Error("SHADOW_INGEST_WS set but READ_ONLY=true; refusing to ingest into the production DB")
 				os.Exit(1)
 			}
-			srv.ingestor = newIngestor(pool, logger, srv.hub.broadcast)
+			srv.ingestor = newIngestor(pool, logger, srv.hub.broadcast, srv.plugins)
 			go srv.runShadowConsumer(ctx, cfg.IngestWS)
 			logger.Info("shadow ingest enabled", "source", cfg.IngestWS)
 		}