fix: increase retry attempts and waiting time

- Increase retry attempts from 3 to 8
- Increase exponential backoff from 1-10s to 2-120s

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: CLRafaelR

paperbanana/providers/vlm/gemini.py

@@ -49,7 +49,7 @@ def _get_client(self):
     def is_available(self) -> bool:
         return self._api_key is not None
 
-    @retry(stop=stop_after_attempt(3), wait=wait_exponential(min=1, max=10))
+    @retry(stop=stop_after_attempt(8), wait=wait_exponential(min=2, max=120))
     async def generate(
         self,
         prompt: str,