refactor(bot): share image attachment uploads

[RSO]

Summary

• Extract shared Cloud Agent attachment filename/key and PutObject construction into the R2 attachments helper.
• Reuse the shared upload helper for Slack bot image attachments so direct uploads follow the same R2 conventions as presigned Cloud Agent uploads.

Verification

N/A

Visual Changes

N/A

Reviewer Notes

Follow-up to #2749 (comment).

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (2 files)

• apps/web/src/lib/bot/images.ts
• apps/web/src/lib/r2/cloud-agent-attachments.ts

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_{Reviewed by gpt-5.5-2026-04-23 · 266,847 tokens}