chore(oss): audit the server package and resync the SDK mirrors

Split the 657-line operation service into eor, submit, and verify
modules, add the AGENT_REVOKED and KEY_RETIRED codes the Backend already
emits, and condense every multi-line comment. Mirror Node, Python, and
Go at 2.1.0 with the deep-health 503, non-idempotent retry, rotation
grace, and path-encoding fixes. Document which routes and response
fields the self-hosted server does not provide.

Claude-Session: https://claude.ai/code/session_01Agoc9bRVE9KL7mmWtey9Vq

sdks/go/admin_events.go

@@ -0,0 +1,16 @@
+package elydora
+
+import "fmt"
+
+// ListAdminEvents retrieves recent administrative events; limit 0 uses the server default.
+func (c *Client) ListAdminEvents(limit int) (*ListAdminEventsResponse, error) {
+	path := "/v1/admin/events"
+	if limit > 0 {
+		path = fmt.Sprintf("%s?limit=%d", path, limit)
+	}
+	var result ListAdminEventsResponse
+	if err := c.doGet(path, &result); err != nil {
+		return nil, err
+	}
+	return &result, nil
+}