fix: increase LOOKBACK_HOURS to 48 and add Stacker_Sports sub to radar (Bounty #43)

[malsony]

Summary

• Increased LOOKBACK_HOURS from 24 to 48 to allow older items to be considered (the OPEN_BOUNTY item is ~34 hours old)
• Added "Stacker_Sports" to the SUBS list so the radar scans that sub
• This ensures the OPEN_BOUNTY item (id 1490676) is captured and tagged with OPEN_BOUNTY

Changes

• Modified scripts/sn_opportunity_radar.mjs:
  • Changed LOOKBACK_HOURS to 48
  • Added "Stacker_Sports" to SUBS array

Test Plan

• Ran the script with --json and verified that item 1490676 appears with OPEN_BOUNTY tag
• Verified that the item's ageHours is about 34.3, which is less than 48

Closes #43

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