feat: initial Go/JS/Rust Origin check-in client SDKs

Standalone clients that resolve a machine unique ID (OS machine ID first,
falling back to a generated UUID persisted to disk), detect hostname/IP/
container/orchestrator, and register+re-ping origin.warky.dev's public
service-checkin endpoint on a daily interval. Ported from icy2's internal
origincheckin package but extended to the full check-in contract and made
dependency-light for external reuse.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

go/payload.go

@@ -0,0 +1,35 @@
+package originclient
+
+// Payload is the JSON body posted to Origin's public service-checkin
+// endpoint. Field names and requiredness mirror
+// POST /api/public/service-checkin as documented in
+// origin/doc/service-checkin.md: Type, Version, Name, and UniqueInstallID
+// are required; everything else is optional and, when omitted, does not
+// overwrite existing instance data on Origin's side.
+type Payload struct {
+	Type            string `json:"type"`
+	Version         string `json:"version"`
+	Name            string `json:"name"`
+	UniqueInstallID string `json:"unique_install_id"`
+	Site            string `json:"site,omitempty"`
+	Environment     string `json:"environment,omitempty"`
+	DatabaseType    string `json:"database_type,omitempty"`
+	DatabaseName    string `json:"database_name,omitempty"`
+	AppType         string `json:"app_type,omitempty"`
+	Hostname        string `json:"hostname,omitempty"`
+	Port            int    `json:"port,omitempty"`
+	BaseURL         string `json:"base_url,omitempty"`
+	InternalURL     string `json:"internal_url,omitempty"`
+	ContainerID     string `json:"container_id,omitempty"`
+	Orchestrator    string `json:"orchestrator,omitempty"`
+	Description     string `json:"description,omitempty"`
+}
+
+// Response is returned by Origin after a successful check-in.
+type Response struct {
+	Success           bool   `json:"success"`
+	ServiceInstanceID int64  `json:"service_instance_id"`
+	UniqueInstallID   string `json:"unique_install_id"`
+	Status            string `json:"status"`
+	PingedAt          string `json:"pinged_at"`
+}