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.

.vscode/tasks.json

@@ -0,0 +1,49 @@
+{
+  "version": "2.0.0",
+  "tasks": [
+    {
+      "label": "dev: ensure .dev/site.env",
+      "type": "npm",
+      "script": "dev:env",
+      "problemMatcher": []
+    },
+    {
+      "label": "dev: seed placeholder menus",
+      "type": "npm",
+      "script": "seed",
+      "problemMatcher": []
+    },
+    {
+      "label": "dev: watch server",
+      "type": "npm",
+      "script": "dev",
+      "problemMatcher": []
+    },
+    {
+      "label": "test",
+      "type": "npm",
+      "script": "test",
+      "group": { "kind": "test", "isDefault": true },
+      "problemMatcher": []
+    },
+    {
+      "label": "typecheck",
+      "type": "npm",
+      "script": "typecheck",
+      "group": { "kind": "build", "isDefault": true },
+      "problemMatcher": ["$tsc"]
+    },
+    {
+      "label": "verify the data directory",
+      "type": "npm",
+      "script": "verify",
+      "problemMatcher": []
+    },
+    {
+      "label": "repair missing derivatives",
+      "type": "npm",
+      "script": "repair",
+      "problemMatcher": []
+    }
+  ]
+}