feat: add a bulk sign-out-all-other-sessions action to security settings (Closes #743)

[waterWang]

Summary

Adds a sign-out-all-other-sessions bulk revoke action to the security settings, distinct from the per-session revoke control.

Changes

• Per-session revoke: Each non-current session row now shows a Sign out button (with LogOut icon) that removes that single session
• Bulk action: Renamed from "Sign out all sessions" to "Sign out all other sessions". The confirmation dialog explicitly states the current session is not affected
• State management: Sessions are now tracked as state (not a static array), so revoking one or all updates the UI immediately
• Confirmation copy: Updated dialog title/description/impact items to clarify that the current device remains signed in
• Tests: Added new tests covering per-session sign-out, current-session protection, session count badge, and bulk sign-out flow

QA

• Per-session sign-out button is shown only for non-current sessions
• Clicking per-session sign-out removes the session and updates the badge count
• Bulk sign-out (requires typing "LOGOUT") removes all non-current sessions
• Current session is preserved after both individual and bulk revoke
• All 97 tests pass (no regressions)

[vercel]

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