feat(macroplan): vendor plan model and grid from the macroplan app

Copied verbatim (imports resorted) from jclab/macroplan so future
upstream syncs stay copy-paste; extraction to a shared package is
deferred until drift hurts.

package.json

@@ -60,6 +60,8 @@
     "retrobus": "^1.9.4",
     "sanitize-html": "^2.17.0",
     "shikiji-core": "0.10.2",
+    "smol-toml": "^1.7.0",
+    "valibot": "^1.4.2",
     "vue": "^3.5.18",
     "vue-i18n": "^11.1.11",
     "vue-router": "^4.5.1",