chore(go): audit providers claudecode codex cursor gemini

Add managed_runtime.go (paths, config validation, identity, runtime file
changes, status checks) and shell_command.go (quoting, PowerShell
encoding, command parsing) and move the four providers onto them.

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

cmd/elydora/plugins/claudecode_contract.go

@@ -77,11 +77,7 @@ type claudeRenderedDocument struct {
 	remove   bool
 }
 
-type claudeRuntimeContract struct {
-	agentID   string
-	guardPath string
-	auditPath string
-}
+type claudeRuntimeContract = managedRuntimeContract
 
 func cloneClaudeObject(value map[string]any) map[string]any {
 	clone := make(map[string]any, len(value))