chore: bump analyze cache TTL from 5 min to 24 hours

Directory structure of a repo barely changes (new package added maybe
once a month). 24hr cache saves GitHub API calls at ~3-5KB per entry.
1000 cached repos = 5MB Redis. Effectively free.

Author: DevanshuNEU

backend/routes/repos.py

@@ -295,7 +295,7 @@ def validate_url(cls, v: str) -> str:
         return v
 
 
-_ANALYZE_CACHE_TTL = 300  # 5 minutes, same as validate-repo
+_ANALYZE_CACHE_TTL = 86400  # 24 hours -- directory structure rarely changes
 
 
 @router.post("/analyze")