perf(teams): batch ownership checks in LegacyRemoveMemberService

[diogeneszilli]

Summary

• Replace nested Promise.all().map() calling isTeamOwner() per member per team (M×T×2 queries) with a single membership.findMany() batch query
• Build an in-memory Set for O(1) ownership lookups instead of repeated DB round-trips

Test plan

• Verify that non-owners cannot remove team owners
• Verify that owners cannot remove themselves from teams they own
• Verify org admins bypass ownership checks as before
• Run yarn type-check:ci --force to confirm no type regressions

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