feat: implement Havenllo single-board kanban (Go+SQLite backend, Preact/Vite frontend)

- Single fixed 'Haven' board: lists (To do/In progress/Done) + cards, no multi-board
- Go 1.24 backend, CGO-free modernc.org/sqlite, embedded SPA, REST /api
- Preact + Vite + TS frontend, native HTML5 drag-and-drop, optimistic UI, dark Haven theme
- PVC (nfs-client) for SQLite, root container on NFS, simple nginx ingress havenllo.haven
- Dockerfile multi-arch build, Gitea CI via pipeline-actions@main

cmd/havenllo/main.go

@@ -0,0 +1,57 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"log"
+	"net/http"
+	"os"
+	"os/signal"
+	"syscall"
+	"time"
+
+	"havenllo/internal/api"
+	"havenllo/internal/app"
+	"havenllo/internal/database"
+	"havenllo/web"
+)
+
+func main() {
+	listenAddr := env("HAVENLLO_LISTEN_ADDR", ":8080")
+	databasePath := env("HAVENLLO_DATABASE_PATH", "/data/havenllo.db")
+
+	ctx := context.Background()
+	db, err := database.Open(ctx, databasePath)
+	if err != nil {
+		log.Fatalf("database setup failed: %v", err)
+	}
+	defer db.Close()
+
+	server := &http.Server{
+		Addr:              listenAddr,
+		Handler:           api.NewHandler(app.New(db), web.Files),
+		ReadHeaderTimeout: 10 * time.Second,
+	}
+	go func() {
+		log.Printf("Havenllo listening on %s", listenAddr)
+		if err := server.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
+			log.Fatalf("server failed: %v", err)
+		}
+	}()
+
+	stop := make(chan os.Signal, 1)
+	signal.Notify(stop, os.Interrupt, syscall.SIGTERM)
+	<-stop
+	shutdownCtx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+	if err := server.Shutdown(shutdownCtx); err != nil {
+		log.Printf("graceful shutdown failed: %v", err)
+	}
+}
+
+func env(key, fallback string) string {
+	if value := os.Getenv(key); value != "" {
+		return value
+	}
+	return fallback
+}