feat: add multi-host assignment for round robin bookings

[pedroccastro]

What does this PR do?

This PR implements a new feature for Round Robin event types: optional multi-host assignment per booking.

Current behavior:

• Round Robin always assigns exactly 1 host per booking
• Collective requires all hosts to be available

New behavior:

• New maxRoundRobinHosts config (1-20, default: 1)
• Uses union availability (same as current RR logic)
• At booking confirmation, assigns up to N available hosts
• Minimum always 1 (preserves default RR behavior)

Example scenario:

• Event type has 5 interviewers
• Candidate selects a time where 4 are available
• If maxRoundRobinHosts = 3 → 3 hosts automatically assigned

Fixes #25491 | Linear: CAL-6840

Key Changes:

Layer	File(s)	Change
Schema	schema.prisma	Add maxRoundRobinHosts Int? with Zod validation
API v2	DTOs (create, update, output)	Add field with @Min(1) @Max(20) validation
Booking Logic	RegularBookingService.ts	Use getOrderedListOfLuckyUsers() for multi-host selection
tRPC	eventTypeRepository.ts	Add field to select statements
Form	useEventTypeForm.ts	Add to defaultValues
UI	EventTeamAssignmentTab.tsx	Add NumberInput for configuration
i18n	common.json	Add translation keys

Visual Demo

UI - New configuration field in Round Robin Hosts section

Booking result - Multiple hosts assigned

How should this be tested?

Test Scenario 1 - Multi-host assignment:

1. Create Round Robin event type with 3+ hosts
2. Set maxRoundRobinHosts = 3
3. Create a booking when all hosts are available
4. Expected: Booking created with 3 hosts assigned

Test Scenario 2 - Partial availability:

1. Round Robin with maxRoundRobinHosts = 4
2. Only 2 hosts available at selected time
3. Expected: Booking created with 2 hosts (assigns all available up to max)

Test Scenario 3 - Default behavior (regression):

1. Create Round Robin event type
2. Leave maxRoundRobinHosts empty (null/default)
3. Create booking
4. Expected: Only 1 host assigned (existing behavior preserved)

Performance improvements

• Replace N calls to getLuckyUser() with single getOrderedListOfLuckyUsers() call (reduces DB queries from O(n) to O(1) per group)
• Parallelize recurring slot availability checks with Promise.all
• Pre-compute enrichedHosts, userIdsSet, and firstUserOrgId outside loops

Mandatory Tasks

• [x] I have self-reviewed the code
• [x] I have updated the developer docs in /docs if this PR makes changes that would require a documentation change.
• [x] I confirm automated tests are in place that prove my fix is effective or that my feature works.

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Project	Deployment	Review	Updated (UTC)
cal-companion	Ready	Preview, Comment	Dec 16, 2025 2:48pm

2 Skipped Deployments

Project	Deployment	Review	Updated (UTC)
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