Initial commit: img-infinite-canvas AI design workbench MVP

Moteva-style AI design workbench replica. Home prompt creates a project;
the project page provides an infinite canvas with node drag, zoom/pan,
a design chat panel, history replay, image asset upload, and project
save/regenerate.

- Backend: go-zero, DDD layering, sqlc/pgx, optional PostgreSQL; memory
  or Redis cache; asynq job queue; MinIO/S3/R2/OSS object storage;
  sky-valley/pi agent runtime adapter.
- Frontend: Next.js App Router + Vite artifact build, TypeScript, i18n,
  shadcn/ui components, auth (OTP/Turnstile/Google/WeChat).
- Deploy: Docker Compose and k3s manifests.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/internal/logic/prompt_validation.go

@@ -0,0 +1,38 @@
+package logic
+
+import (
+	"fmt"
+	"strings"
+
+	"img_infinite_canvas/internal/domain/design"
+)
+
+func validateRequiredPrompt(prompt string, allowEmpty bool) error {
+	if allowEmpty {
+		return nil
+	}
+	if hasRequiredPromptText(prompt) {
+		return nil
+	}
+	return fmt.Errorf("%w: prompt is required", design.ErrInvalidInput)
+}
+
+func hasRequiredPromptText(prompt string) bool {
+	for _, line := range strings.Split(prompt, "\n") {
+		line = strings.TrimSpace(strings.ReplaceAll(line, "\u00a0", " "))
+		if line == "" || isPromptReferenceDirective(line) {
+			continue
+		}
+		return true
+	}
+	return false
+}
+
+func isPromptReferenceDirective(line string) bool {
+	lower := strings.ToLower(line)
+	hasURL := strings.Contains(lower, "http://") || strings.Contains(lower, "https://")
+	if !hasURL {
+		return false
+	}
+	return strings.HasPrefix(line, "参考图") || strings.HasPrefix(lower, "reference image")
+}