Vendor every dependency, so no build fetches the host's validator (hq to-be 45 D1)

The controller imports mesh-host/validate through a replace onto the forge
that holds it, and every build — the build agent's go build in a fresh
toolchain container, the Dockerfile's go mod download — would have fetched
it through the public proxy and checksum database at build time: a merge
breaking main on the network, the class Phase 1 removes. vendor/ is
committed; go builds from it with nothing fetched, and refuses to build
when it and go.mod disagree, so a pin moved without go mod vendor fails at
once. The Dockerfile copies vendor/ and builds with GOPROXY=off.

vendor/github.com/jackc/pgx/v5/pgproto3/copy_data.go

@@ -0,0 +1,67 @@
+package pgproto3
+
+import (
+	"encoding/hex"
+	"encoding/json"
+)
+
+type CopyData struct {
+	Data []byte
+}
+
+// Backend identifies this message as sendable by the PostgreSQL backend.
+func (*CopyData) Backend() {}
+
+// Frontend identifies this message as sendable by a PostgreSQL frontend.
+func (*CopyData) Frontend() {}
+
+// Decode decodes src into dst. src must contain the complete message with the exception of the initial 1 byte message
+// type identifier and 4 byte message length.
+func (dst *CopyData) Decode(src []byte) error {
+	dst.Data = src
+	return nil
+}
+
+// Encode encodes src into dst. dst will include the 1 byte message type identifier and the 4 byte message length.
+func (src *CopyData) Encode(dst []byte) ([]byte, error) {
+	dst, sp := beginMessage(dst, 'd')
+	dst = append(dst, src.Data...)
+	return finishMessage(dst, sp)
+}
+
+// MarshalJSON implements encoding/json.Marshaler.
+func (src CopyData) MarshalJSON() ([]byte, error) {
+	return json.Marshal(struct {
+		Type string
+		Data string
+	}{
+		Type: "CopyData",
+		Data: hex.EncodeToString(src.Data),
+	})
+}
+
+// UnmarshalJSON implements encoding/json.Unmarshaler.
+func (dst *CopyData) UnmarshalJSON(data []byte) error {
+	// Ignore null, like in the main JSON package.
+	if string(data) == "null" {
+		return nil
+	}
+
+	var msg struct {
+		Data string
+	}
+	if err := json.Unmarshal(data, &msg); err != nil {
+		return err
+	}
+
+	if msg.Data == "" {
+		dst.Data = []byte{}
+		return nil
+	}
+	b, err := hex.DecodeString(msg.Data)
+	if err != nil {
+		return err
+	}
+	dst.Data = b
+	return nil
+}