3D 提交计划在非 3D 模式改用专门的原因文案

- src/components/image-editor/model3d-generation/Model3dGenerationSubmission.ts：buildModel3dSubmissionPlan 的 mode 兜底改用 MODEL3D_MODE_UNSUPPORTED_REASON，不再把非 3D 面板说成「3D 模型定价尚未配置」

验证：npx vitest run src/components/image-editor/model3d-generation

src/components/image-editor/model3d-generation/Model3dGenerationSubmission.ts

@@ -11,7 +11,7 @@ import {
   DEFAULT_MODEL3D_MODEL_VERSION,
   isModel3dGenerationMode,
   mintModel3dAttemptNonce,
-  MODEL3D_PRICING_UNAVAILABLE_REASON,
+  MODEL3D_MODE_UNSUPPORTED_REASON,
   resolveModel3dEndpoint,
   resolveModel3dGenerationParams,
   resolveModel3dGenerationQuote,
@@ -75,7 +75,7 @@ export function buildModel3dSubmissionPlan({
   pricing?: Model3dPricingConfig | null;
 }): { ok: true; plan: Model3dSubmissionPlan } | { ok: false; message: string } {
   if (!isModel3dGenerationMode(dialog.mode)) {
-    return { ok: false, message: MODEL3D_PRICING_UNAVAILABLE_REASON };
+    return { ok: false, message: MODEL3D_MODE_UNSUPPORTED_REASON };
   }
   const trimmedProjectId = projectId?.trim();
   if (!trimmedProjectId) {