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/golang-migrate/migrate/v4/.golangci.yml

@@ -0,0 +1,30 @@
+run:
+  # timeout for analysis, e.g. 30s, 5m, default is 1m
+  timeout: 5m
+linters:
+  enable:
+    #- golint
+    #- interfacer
+    - unconvert
+    #- dupl
+    - goconst
+    - gofmt
+    - misspell
+    - unparam
+    - nakedret
+    - prealloc
+    - revive
+    #- gosec
+linters-settings:
+  misspell:
+    locale: US
+  revive:
+    rules:
+      - name: redundant-build-tag
+issues:
+  max-same-issues: 0
+  max-issues-per-linter: 0
+  exclude-use-default: false
+  exclude:
+    # gosec: Duplicated errcheck checks
+    - G104