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>

backend/internal/config/config.go

@@ -0,0 +1,30 @@
+package config
+
+import (
+	"os"
+)
+
+// Config holds application configuration loaded from the environment.
+type Config struct {
+	DatabaseURL string
+	Port        string
+}
+
+// Load reads configuration from environment variables.
+// DATABASE_URL is required; PORT defaults to "3000".
+func Load() *Config {
+	dbURL := os.Getenv("DATABASE_URL")
+	if dbURL == "" {
+		dbURL = "postgres://osdb:osdb@localhost:5432/osdb?sslmode=disable"
+	}
+
+	port := os.Getenv("PORT")
+	if port == "" {
+		port = "3000"
+	}
+
+	return &Config{
+		DatabaseURL: dbURL,
+		Port:        port,
+	}
+}