Add Nix flake for mcp and mcp-agent

Exposes two packages:
- default (mcp CLI) for operator workstations
- mcp-agent for managed nodes

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/golang.org/x/text/secure/bidirule/bidirule10.0.0.go

@@ -0,0 +1,11 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build go1.10
+
+package bidirule
+
+func (t *Transformer) isFinal() bool {
+	return t.state == ruleLTRFinal || t.state == ruleRTLFinal || t.state == ruleInitial
+}