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/cmd/elydora/plugins/registry.go

@@ -26,8 +26,7 @@ var SupportedAgents = map[string]AgentRegistryEntry{
 	"qwen":       {Name: "Qwen Code", ConfigDir: "~/.qwen", ConfigFile: "settings.json"},
 }
 
-// NewPlugin creates a plugin instance for the given agent name.
-// Returns nil if the agent is not supported.
+// NewPlugin returns the plugin for an agent name, or nil when unsupported.
 func NewPlugin(agentName string) AgentPlugin {
 	switch agentName {
 	case "augment":