chore: initial repository scaffolding

- Add README with features, quick-start (local + Docker) and docs index
- Add MIT LICENSE, root .gitignore and .env.example
- Add docker-compose.yml (postgres + backend + frontend)
- Add root package.json with install:all/dev helpers
- Add Gitea CI workflow (backend syntax check, frontend build)

package.json

@@ -0,0 +1,13 @@
+{
+  "name": "openstack",
+  "version": "0.1.0",
+  "private": true,
+  "description": "Notion-like collaborative workspace (Vue + Express + Postgres)",
+  "scripts": {
+    "install:all": "npm --prefix backend install && npm --prefix frontend install",
+    "dev": "npx concurrently \"npm --prefix backend run dev\" \"npm --prefix frontend run dev\""
+  },
+  "devDependencies": {
+    "concurrently": "^9.0.1"
+  }
+}