feat: enhance canvas and node components with error handling and retry logic

- Integrated retry logic for AI image generation to handle transient errors and improve user experience.
- Updated error categorization to provide more informative feedback based on different failure scenarios.
- Enhanced node components to display retry attempts and error messages, improving visibility during image generation failures.
- Refactored canvas and node components to include retry count in status updates, ensuring accurate tracking of generation attempts.

convex/schema.ts

@@ -183,6 +183,7 @@ export default defineSchema({
     // Node-Status (UX-Strategie: Status direkt am Node sichtbar)
     status: nodeStatus,
     statusMessage: v.optional(v.string()),         // z.B. "Timeout — Credits nicht abgebucht"
+    retryCount: v.optional(v.number()),            // Anzahl bereits durchgeführter Retries
     // Typ-spezifische Daten
     // Convex empfiehlt v.any() für polymorphe data-Felder
     // Type Safety wird über den `type`-Discriminator + Zod im Frontend sichergestellt