Handle unmapped client IDs and respect disabled match uploads

[tintinhamans]

• Handle enum-compatible but unmapped client IDs without returning HTTP 500.
• Respect MatchData.upload_match_data before initializing the S3 client.
• Skip presigned URL generation when match uploads are disabled.
• Return empty upload URLs in lobby and WebSocket responses when uploads are unavailable.

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Enum.TryParse accepts values such as unknown and arbitrary numeric values. These values were not present in the known-client session mapping, causing the login request to return HTTP 500.

The match-data upload toggle was also not honored during S3 initialization or URL generation. Disabling uploads still required valid S3 configuration and attempted to generate upload URLs.