feat: bootstrap OSDB full-stack skeleton (story #01)

- Go backend: Echo v4 + pgxpool + embedded golang-migrate; health endpoints
  at /health and /api/v1/health; TDD health handler (httptest)
- Vue 3 frontend: Vite + TypeScript + Pinia + vue-router + Tailwind CSS v4;
  TDD HelloWorld component (@vue/test-utils + jsdom + vitest)
- Infra: docker-compose postgres:16 with env-interpolated credentials;
  Makefile with dev-db health-wait loop, migrate-up/down, run, test, fmt
- embed.FS migrations at backend/migrations/ (000001 no-op baseline)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/stores/appStore.ts

@@ -0,0 +1,14 @@
+import { defineStore } from 'pinia'
+import { ref } from 'vue'
+
+// appStore: global application state stub.
+// Extended by later stories (auth, fruit, publication stores).
+export const useAppStore = defineStore('app', () => {
+  const ready = ref(false)
+
+  function setReady(value: boolean) {
+    ready.value = value
+  }
+
+  return { ready, setReady }
+})