Add Nix flake for mciasctl and mciasgrpcctl

Vendor dependencies and expose control program binaries via
nix build. Uses nixpkgs-unstable for Go 1.26 support.

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

vendor/github.com/pelletier/go-toml/v2/unstable/kind.go

@@ -0,0 +1,71 @@
+package unstable
+
+import "fmt"
+
+// Kind represents the type of TOML structure contained in a given Node.
+type Kind int
+
+const (
+	// Meta
+	Invalid Kind = iota
+	Comment
+	Key
+
+	// Top level structures
+	Table
+	ArrayTable
+	KeyValue
+
+	// Containers values
+	Array
+	InlineTable
+
+	// Values
+	String
+	Bool
+	Float
+	Integer
+	LocalDate
+	LocalTime
+	LocalDateTime
+	DateTime
+)
+
+// String implementation of fmt.Stringer.
+func (k Kind) String() string {
+	switch k {
+	case Invalid:
+		return "Invalid"
+	case Comment:
+		return "Comment"
+	case Key:
+		return "Key"
+	case Table:
+		return "Table"
+	case ArrayTable:
+		return "ArrayTable"
+	case KeyValue:
+		return "KeyValue"
+	case Array:
+		return "Array"
+	case InlineTable:
+		return "InlineTable"
+	case String:
+		return "String"
+	case Bool:
+		return "Bool"
+	case Float:
+		return "Float"
+	case Integer:
+		return "Integer"
+	case LocalDate:
+		return "LocalDate"
+	case LocalTime:
+		return "LocalTime"
+	case LocalDateTime:
+		return "LocalDateTime"
+	case DateTime:
+		return "DateTime"
+	}
+	panic(fmt.Errorf("Kind.String() not implemented for '%d'", k))
+}