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>

rust/src/payload.rs

@@ -0,0 +1,50 @@
+use serde::{Deserialize, Serialize};
+
+/// 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
+/// `unique_install_id` are required; everything else is optional and, when
+/// omitted, does not overwrite existing instance data on Origin's side.
+#[derive(Debug, Clone, Default, Serialize)]
+pub struct Payload {
+    #[serde(rename = "type")]
+    pub type_: String,
+    pub version: String,
+    pub name: String,
+    pub unique_install_id: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub site: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub environment: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub database_type: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub database_name: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub app_type: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub hostname: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub port: Option<u16>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub base_url: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub internal_url: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub container_id: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub orchestrator: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub description: Option<String>,
+}
+
+/// CheckinResponse is returned by Origin after a successful check-in.
+#[derive(Debug, Clone, Deserialize)]
+pub struct CheckinResponse {
+    pub success: bool,
+    pub service_instance_id: i64,
+    pub unique_install_id: String,
+    pub status: String,
+    pub pinged_at: String,
+}