[Feature]: Unify match, tournament, and series creation in a single event-creation flow

[voyager-slama]

Is your feature request related to a problem?

Replace separate creation pages with one event-creation flow that branches based on the chosen event type.

Describe the solution you'd like

A unified entry point should reduce duplicated UI and simplify onboarding.

Additional context

A unified entry point should reduce duplicated UI and simplify onboarding.

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Migrated from Todoist by voyager[bot].