Make dev mode one command and add VS Code config

npm run dev now runs scripts/dev-env.ts first, which creates .dev/site.env with
a known dev password and a random session secret, so a fresh clone serves a
working admin without anyone hand-building a hash. Adds .vscode launch
configurations and tasks for the dev server, one test file, and check-site, and
brings scripts/ under typecheck, which it had been missing.

tsconfig.json

@@ -18,5 +18,5 @@
     "skipLibCheck": true,
     "types": ["node"]
   },
-  "include": ["src/**/*.ts", "test/**/*.ts"]
+  "include": ["src/**/*.ts", "test/**/*.ts", "scripts/**/*.ts"]
 }