fix(inbox): pluralize Scout label in signal source dropdown

[andrewm4894]

Summary

• The signal source dropdown in the Inbox showed "Scout"; it should read "Scouts".
• Updated the signals_scout option label in INBOX_SOURCE_OPTIONS.

Notes

This is a copy-only change to the dropdown label; the underlying signals_scout value and backend contract are unchanged.

🤖 Generated with Claude Code

[github-actions]

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[github-actions]

Purely cosmetic label text change in a UI filter dropdown — no logic, contracts, or data models affected.

[greptile-apps]

_{Reviews (1): Last reviewed commit: "fix(inbox): pluralize Scout label in sig..." | Re-trigger Greptile}