parquet_pushdown(M0-C4): wire the weed pushdown subcommand

Add weed/command/pushdown.go that parses CLI flags (-filer, -ip,
-port, -trust, -dev.connector_trusted_ack), assembles a daemon.Config,
and calls daemon.Run. Default port 18888 is unused elsewhere in the
SeaweedFS port table and is far enough above the filer/master/volume
ports to be unsurprising in operations. Long help spells out the two
trust modes and points the operator at PARQUET_PUSHDOWN_DESIGN.md and
PARQUET_PUSHDOWN_DEV_PLAN.md for context.

Register cmdPushdown in weed/command/command.go's Commands list so
"weed pushdown" appears in the top-level help. The command is gated
"<WIP>" until later milestones land actual pruning behavior.

weed/command/command.go

@@ -37,6 +37,7 @@ var Commands = []*Command{
 	cmdMqAgent,
 	cmdMqBroker,
 	cmdMqKafkaGateway,
+	cmdPushdown,
 	cmdS3,
 	cmdScaffold,
 	cmdServer,

weed/command/pushdown.go

@@ -0,0 +1,71 @@
+package command
+
+import (
+	"github.com/seaweedfs/seaweedfs/weed/glog"
+	"github.com/seaweedfs/seaweedfs/weed/parquet_pushdown"
+	"github.com/seaweedfs/seaweedfs/weed/parquet_pushdown/daemon"
+	"github.com/seaweedfs/seaweedfs/weed/pb"
+	"github.com/seaweedfs/seaweedfs/weed/util"
+	"github.com/seaweedfs/seaweedfs/weed/util/version"
+)
+
+var (
+	pushdownOptions PushdownOptions
+)
+
+type PushdownOptions struct {
+	filer               *string
+	ip                  *string
+	port                *int
+	trustMode           *string
+	connectorTrustedAck *bool
+}
+
+func init() {
+	cmdPushdown.Run = runPushdown // break init cycle
+	pushdownOptions.filer = cmdPushdown.Flag.String("filer", "localhost:8888", "comma-separated filer server addresses for high availability")
+	pushdownOptions.ip = cmdPushdown.Flag.String("ip", util.DetectedHostAddress(), "pushdown daemon gRPC listen ip address")
+	pushdownOptions.port = cmdPushdown.Flag.Int("port", 18888, "pushdown daemon gRPC listen port")
+	pushdownOptions.trustMode = cmdPushdown.Flag.String("trust", string(parquet_pushdown.TrustModeCatalogValidated), "trust mode: catalog-validated (default) or connector-trusted (dev only)")
+	pushdownOptions.connectorTrustedAck = cmdPushdown.Flag.Bool("dev.connector_trusted_ack", false, "explicitly acknowledge running with -trust=connector-trusted; required for that mode")
+}
+
+var cmdPushdown = &Command{
+	UsageLine: "pushdown [-port=18888] [-filer=<ip:port>[,<ip:port>]...] [-trust=catalog-validated]",
+	Short:     "<WIP> start the SeaweedFS Parquet pushdown daemon (M0 skeleton)",
+	Long: `start the SeaweedFS Parquet pushdown daemon.
+
+	The pushdown daemon is a standalone gRPC service that accelerates Parquet/
+	Iceberg scans by pruning files, row groups, and pages before the engine
+	reads data. See PARQUET_PUSHDOWN_DESIGN.md and PARQUET_PUSHDOWN_DEV_PLAN.md
+	at the repo root for the full design and milestone plan.
+
+	M0 ships request validation and the gRPC surface only; pruning logic
+	lands in M1+.
+
+	Trust modes:
+	  catalog-validated (default)
+	      Server validates each request's DataFiles and Deletes against the
+	      Iceberg catalog at the requested snapshot before serving.
+	  connector-trusted
+	      Skip catalog validation. Developer-only; production builds must
+	      not enable. Requires the explicit -dev.connector_trusted_ack flag.
+
+	Multiple filer addresses can be specified for high availability,
+	separated by commas.`,
+}
+
+func runPushdown(cmd *Command, args []string) bool {
+	cfg := daemon.Config{
+		IP:                  *pushdownOptions.ip,
+		Port:                *pushdownOptions.port,
+		FilerAddresses:      pb.ServerAddresses(*pushdownOptions.filer).ToAddresses(),
+		TrustMode:           parquet_pushdown.TrustMode(*pushdownOptions.trustMode),
+		ConnectorTrustedAck: *pushdownOptions.connectorTrustedAck,
+		Version:             version.Version(),
+	}
+	if err := daemon.Run(cfg); err != nil {
+		glog.Fatalf("pushdown daemon: %v", err)
+	}
+	return true
+}