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/cmd/server/main.go

@@ -0,0 +1,75 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+	"os/signal"
+	"syscall"
+	"time"
+
+	"osdb/internal/config"
+	"osdb/internal/database"
+	"osdb/internal/migrate"
+)
+
+func main() {
+	cfg := config.Load()
+
+	args := os.Args[1:]
+
+	switch {
+	case len(args) >= 1 && args[0] == "migrate":
+		if len(args) >= 2 && args[1] == "down" {
+			if err := migrate.Down(cfg.DatabaseURL); err != nil {
+				log.Fatalf("migrate down: %v", err)
+			}
+			log.Println("migrate down: done")
+		} else {
+			if err := migrate.Up(cfg.DatabaseURL); err != nil {
+				log.Fatalf("migrate up: %v", err)
+			}
+			log.Println("migrate up: applied")
+		}
+		return
+	default:
+		serve(cfg)
+	}
+}
+
+func serve(cfg *config.Config) {
+	ctx := context.Background()
+
+	pool, err := database.Connect(ctx, cfg.DatabaseURL)
+	if err != nil {
+		log.Fatalf("database connect: %v", err)
+	}
+	defer pool.Close()
+	log.Println("database: connected")
+
+	e := New(pool)
+
+	// Start server
+	go func() {
+		addr := fmt.Sprintf(":%s", cfg.Port)
+		log.Printf("server: listening on %s", addr)
+		if err := e.Start(addr); err != nil && err != http.ErrServerClosed {
+			log.Fatalf("server: %v", err)
+		}
+	}()
+
+	// Graceful shutdown on SIGINT / SIGTERM
+	quit := make(chan os.Signal, 1)
+	signal.Notify(quit, syscall.SIGINT, syscall.SIGTERM)
+	<-quit
+
+	log.Println("server: shutting down")
+	shutdownCtx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+
+	if err := e.Shutdown(shutdownCtx); err != nil {
+		log.Printf("server: shutdown error: %v", err)
+	}
+}