fix: revert all-provider cost tracking and hide indicator for audio nodes

Restore fal-only cost tracking guard in video/audio executors — other
providers don't have reliable pricing. Also add generateAudio to
hasNonGeminiProviders so the CostIndicator hides when audio nodes
are present.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/store/execution/generateAudioExecutor.ts

@@ -141,7 +141,7 @@ export async function executeGenerateAudio(
       });
 
       // Track cost
-      if (nodeData.selectedModel?.pricing) {
+      if (nodeData.selectedModel?.provider === "fal" && nodeData.selectedModel?.pricing) {
         addIncurredCost(nodeData.selectedModel.pricing.amount);
       }
 

src/store/execution/generateVideoExecutor.ts

@@ -148,7 +148,7 @@ export async function executeGenerateVideo(
       });
 
       // Track cost
-      if (nodeData.selectedModel?.pricing) {
+      if (nodeData.selectedModel?.provider === "fal" && nodeData.selectedModel?.pricing) {
         addIncurredCost(nodeData.selectedModel.pricing.amount);
       }
 

src/utils/costCalculator.ts

@@ -258,6 +258,9 @@ export function hasNonGeminiProviders(nodes: WorkflowNode[]): boolean {
       const data = node.data as Generate3DNodeData;
       return data.selectedModel?.provider !== undefined && data.selectedModel.provider !== "gemini";
     }
+    if (node.type === "generateAudio") {
+      return true; // Audio nodes are always non-Gemini
+    }
     return false;
   });
 }