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/codex_test.go

@@ -355,10 +355,10 @@ func TestCodexUninstallPreservesUnrelatedHooksAndExactAgent(t *testing.T) {
 	if len(requireArray(t, hooks["PreToolUse"])) != 2 || len(requireArray(t, hooks["PostToolUse"])) != 1 {
 		t.Fatalf("unexpected remaining hooks: %#v", hooks)
 	}
-	_, remainingScript, parsed := parseCodexPOSIXCommand(
-		requireCodexHandler(t, remaining, "PostToolUse", codexAuditStatus)["command"],
+	_, remainingScript, parsed := parsePOSIXCommand(
+		requireCodexHandler(t, remaining, "PostToolUse", codexAuditStatus)["command"].(string),
 	)
-	if !parsed || !sameCodexPath(remainingScript, filepath.Join(otherDir, codexAuditScript)) {
+	if !parsed || !sameManagedPath(remainingScript, filepath.Join(otherDir, codexAuditScript)) {
 		t.Fatalf("other agent handler was removed: %#v", hooks)
 	}
 }