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/database/sqlite/README.md

@@ -0,0 +1,17 @@
+# sqlite
+
+`sqlite://path/to/database?query`
+
+Unlike other migrate database drivers, the sqlite driver will automatically wrap each migration in an implicit transaction by default.  Migrations must not contain explicit `BEGIN` or `COMMIT` statements.  This behavior may change in a future major release.  (See below for a workaround.)
+
+The auxiliary query parameters listed below may be supplied to tailor migrate behavior.  All auxiliary query parameters are optional.
+
+| URL Query  | WithInstance Config | Description |
+|------------|---------------------|-------------|
+| `x-migrations-table` | `MigrationsTable` | Name of the migrations table.  Defaults to `schema_migrations`. |
+| `x-no-tx-wrap` | `NoTxWrap` | Disable implicit transactions when `true`.  Migrations may, and should, contain explicit `BEGIN` and `COMMIT` statements. |
+
+## Notes
+
+* Uses the `modernc.org/sqlite` sqlite db driver (pure Go)
+  * Has [limited `GOOS` and `GOARCH` support](https://pkg.go.dev/modernc.org/sqlite?utm_source=godoc#hdr-Supported_platforms_and_architectures)