Grant Lambda self-invoke IAM permission for process_repositories fan-out

[hiroshinishio]

Summary

• process_repositories fans out work with one async lambda:InvokeFunction call per repository, but the Lambda execution role did not have permission to invoke itself.
• Added a LambdaSelfInvokeAccess inline policy scoped to the function's own ARN so the fan-out actually runs.

Social Media Post (GitAuto)

Scheduled repository runs now fan out reliably

• Lambda execution role granted self-invoke permission scoped to the function's own ARN
• process_repositories can now launch one async invocation per repo without IAM errors