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

internal/database/database_test.go

@@ -0,0 +1,69 @@
+package database_test
+
+import (
+	"context"
+	"database/sql"
+	"path/filepath"
+	"testing"
+
+	"havenllo/internal/database"
+)
+
+func TestOpenMigratesSeedsAndEnforcesCascade(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+	path := filepath.Join(t.TempDir(), "havenllo.db")
+	db, err := database.Open(ctx, path)
+	if err != nil {
+		t.Fatalf("Open: %v", err)
+	}
+	defer db.Close()
+
+	var count int
+	if err := db.QueryRowContext(ctx, "SELECT COUNT(*) FROM lists").Scan(&count); err != nil {
+		t.Fatal(err)
+	}
+	if count != 3 {
+		t.Fatalf("seeded lists = %d, want 3", count)
+	}
+	var listID int64
+	if err := db.QueryRowContext(ctx, "SELECT id FROM lists ORDER BY position LIMIT 1").Scan(&listID); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := db.ExecContext(ctx, `INSERT INTO cards (list_id, title, description, position, done, created_at, updated_at)
+		VALUES (?, 'test', '', 1024, 0, '2026-01-01T00:00:00Z', '2026-01-01T00:00:00Z')`, listID); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := db.ExecContext(ctx, "DELETE FROM lists WHERE id = ?", listID); err != nil {
+		t.Fatal(err)
+	}
+	if err := db.QueryRowContext(ctx, "SELECT COUNT(*) FROM cards").Scan(&count); err != nil {
+		t.Fatal(err)
+	}
+	if count != 0 {
+		t.Fatalf("cascade left %d cards", count)
+	}
+}
+
+func TestOpenIsIdempotent(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+	path := filepath.Join(t.TempDir(), "havenllo.db")
+	db, err := database.Open(ctx, path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	_ = db.Close()
+	db, err = database.Open(ctx, path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+	var count int
+	if err := db.QueryRowContext(ctx, "SELECT COUNT(*) FROM schema_migrations").Scan(&count); err != nil && err != sql.ErrNoRows {
+		t.Fatal(err)
+	}
+	if count != 1 {
+		t.Fatalf("migrations = %d, want 1", count)
+	}
+}