/claim #18947

Related to #18947.

Problem

Routing for team event types supports inviting attendees, but there is no way to add team members as optional guests who should be invited without affecting host availability/conflict checks.

What this PR does

• adds metadata.optionalGuestTeamMemberIds to event type metadata schema
• adds an “Optional guest team members” multi-select in Advanced settings (team event types)
• gates the setting behind Teams plan and shows upgrade badge when unavailable
• validates optional guest IDs server-side (team-only, accepted members only, deduplicated)
• injects optional team guests only into calendar attendee payloads (not booking conflict logic)
• propagates optional attendee semantics to calendar integrations (Google, Office365, Lark, Feishu) and ICS role mapping (OPT-PARTICIPANT)
• adds tests for:
  • optional guest ID normalization and validation behavior in update handler
  • ICS optional attendee/team-member serialization
• adds new i18n strings for the new setting

Verification

• yarn vitest run packages/emails/lib/generateIcsString.test.ts
• yarn vitest run packages/trpc/server/routers/viewer/eventTypes/heavy/update.handler.test.ts
• yarn vitest run packages/lib/CalendarService.test.ts
• yarn vitest run packages/app-store/googlecalendar/lib/__tests__/CalendarService.test.ts
• yarn tsc --pretty --noEmit -p packages/trpc/tsconfig.json
• yarn tsc --pretty --noEmit -p packages/app-store/tsconfig.json
• yarn tsc --pretty --noEmit -p apps/web/tsconfig.json
• yarn type-check:ci --force (fails in this checkout due pre-existing workspace/environment issues unrelated to this diff, including spawn tsc ENOENT and existing package-level TS failures)

Scope note

This PR is focused on CAL-5091 behavior for optional team-member guests in team event types.

Demo

I will attach a short demo video in a follow-up comment to satisfy bounty requirements.