fix: correct Go time-format tokens for S3 object key date path

[ThiagoBauken]

Problem

GenerateS3Key builds the date segments of every S3 object key with invalid Go time-format tokens:

year := now.Format("2025")
month := now.Format("05")
day := now.Format("25")

Go's reference time is 2006-01-02 15:04:05, so the only valid tokens are 2006 / 01 / 02. 05 is the seconds field, and 2025 / 25 aren't recognized layouts — so media is stored under nonsensical, non-chronological folders (the "month" segment actually renders seconds). This breaks date-based browsing and any S3 lifecycle/retention rule keyed on the object path.

Fix

Use the correct tokens 2006 / 01 / 02.

Testing

• go build ./... ✅
• go vet ./... ✅
• Single file, 3-line change plus an explanatory comment.

[gemini-code-assist]

Code Review

This pull request corrects the Go time formatting layout tokens in s3manager.go from incorrect values ("2025", "05", "25") to the correct reference layout tokens ("2006", "01", "02") to ensure proper chronological folder organization. There are no review comments, and I have no additional feedback to provide.

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[ThiagoBauken]

Closing to consolidate my recent PRs into a smaller, focused set that's easier to review — I'll resubmit the changes grouped together. Sorry for the churn, and thanks!