feat: implement internal credits handling in AI image generation

- Added support for internal credits feature in the generateImage action.
- Conditional reservation of credits based on the INTERNAL_CREDITS_ENABLED environment variable.
- Updated error handling to ensure credits are released or committed only when reservations are made.

convex/ai.ts

@@ -17,6 +17,9 @@ export const generateImage = action({
     aspectRatio: v.optional(v.string()),
   },
   handler: async (ctx, args) => {
+    const internalCreditsEnabled =
+      process.env.INTERNAL_CREDITS_ENABLED === "true";
+
     const apiKey = process.env.OPENROUTER_API_KEY;
     if (!apiKey) {
       throw new Error("OPENROUTER_API_KEY is not set");
@@ -32,13 +35,15 @@ export const generateImage = action({
       throw new Error("User not found");
     }
 
-    const reservationId = await ctx.runMutation(api.credits.reserve, {
+    const reservationId = internalCreditsEnabled
+      ? await ctx.runMutation(api.credits.reserve, {
           estimatedCost: modelConfig.estimatedCostPerImage,
           description: `Bildgenerierung — ${modelConfig.name}`,
           model: modelId,
           nodeId: args.nodeId,
           canvasId: args.canvasId,
-    });
+        })
+      : null;
 
     await ctx.runMutation(api.nodes.updateStatus, {
       nodeId: args.nodeId,
@@ -96,14 +101,18 @@ export const generateImage = action({
         status: "done",
       });
 
+      if (reservationId) {
         await ctx.runMutation(api.credits.commit, {
           transactionId: reservationId,
           actualCost: creditCost,
         });
+      }
     } catch (error) {
+      if (reservationId) {
         await ctx.runMutation(api.credits.release, {
           transactionId: reservationId,
         });
+      }
 
       await ctx.runMutation(api.nodes.updateStatus, {
         nodeId: args.nodeId,