fix(audio): Ensure /tmp/audio exists and fix nixpacks syntax

apps/api/src/routes/ai.ts

@@ -127,6 +127,11 @@ export async function aiRoutes(fastify: FastifyInstance) {
         const buffer = Buffer.from(audioBase64, 'base64');
 
         try {
+            // Ensure the /tmp/audio directory exists because uploadFile falls back to local storage
+            // This prevents ENOENT errors if the container restarted
+            const { mkdir } = require('fs/promises');
+            await mkdir('/tmp/audio', { recursive: true }).catch(() => { });
+
             const url = await uploadFile(buffer, filename, mimeType);
             console.log(`[AI] ✅ Audio stored: ${url}`);
             return { success: true, url };

nixpacks.toml

@@ -1,4 +1,3 @@
 providers = ["node"]
 
-[phases.setup]
-nixPkgs = ["...", "ffmpeg"]
+aptPkgs = ["ffmpeg"]