deps: Update aiohttp requirement from >=3.9.0 to >=3.13.5 (#93)

---
updated-dependencies:
- dependency-name: aiohttp
  dependency-version: 3.13.5
  dependency-type: direct:production
...

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Author: dependabot[bot]

backend/requirements.txt

@@ -10,7 +10,7 @@ pydantic-settings>=2.1.0
 
 # HTTP Client
 httpx>=0.26.0
-aiohttp>=3.9.0
+aiohttp>=3.13.5
 
 # Database
 sqlalchemy>=2.0.25