fix: bound storage response and proxy idle times - #6

Changes

• Limit each S3 response-header wait to 5 seconds per attempt and each complete object transfer to 10 minutes by default; expose -s3-timeout and chart s3Timeout for tuning.
• Return 504 when storage times out before headers; log a stream timeout if it occurs after headers.
• Allow video transfers through Contour HTTPProxy with response: infinity, while closing streams idle for 60 seconds.
• Document the distinction between time to first byte and total transfer time, and test timeouts before headers and during streaming.

Validation

• go test -mod=readonly ./... passed.
• go vet -mod=readonly ./... passed.
• helm lint and helm template passed.