Ignore schedule conflict warnings for cumulative time-limit rounds

[coder13]

Motivation

• Prevent false-positive schedule conflict warnings when two different events' rounds share a cumulative time limit and therefore are expected to run concurrently.

Description

• Added roundsShareCumulativeTimeLimit helper in src/lib/wcif/validation/personAssignmentValidation.ts to detect when two activities belong to rounds that mutually list each other in timeLimit.cumulativeRoundIds.
• Skip reporting overlaps in findConflictingAssignmentsForPerson when roundsShareCumulativeTimeLimit returns true so assignments in such cumulative rounds do not generate conflicts.
• Added a regression test in src/lib/wcif/validation/personAssignmentValidation.test.ts that sets up two events/rounds (e.g., 4BLD/5BLD) with matching cumulativeRoundIds and overlapping times and asserts no conflict is produced.

Testing

• Ran npm run test -- src/lib/wcif/validation/personAssignmentValidation.test.ts in this environment and it failed to execute because the vitest binary was not found in PATH (sh: 1: vitest: not found).
• No other automated test runs were performed in this environment, but a focused unit test covering the new behavior was added to personAssignmentValidation.test.ts.

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Codex Task