feat(international): add manual event foundation for unresolved slots

[aalonsolopez]

Problem or opportunity

International events need to be schedulable before automatic qualification rules exist, especially when slots are unresolved.

Proposed solution

Add registry entries and DTO support for manual international events with unresolved slots that can be scheduled and represented without auto qualification.

UX impact

Affected area: Data registry entries, backend DTOs, frontend display paths touched by competition browser.

Acceptance criteria

• Manual international event entries can exist in the registry.
• Unresolved slots are represented in DTOs without crashing UI consumers.
• Events can be scheduled manually.
• No automatic qualification logic is added.

Scope

Gameplay

Dependencies

Depends on registry loader and frontend competition browser.

Out of scope

Worlds/MSI qualification algorithms and bracket auto-seeding.

Test notes

Add data/DTO tests for unresolved slots and frontend rendering tests for manual event display.

Approval pre-flight

• I searched existing issues and did not find a duplicate.
• I understand maintainers must add status:approved before implementation starts.
• I will branch from development using type/lowercase-slug if this is approved.
• I identified whether this changes docs, release behavior, licensing, or data provenance.

[NicoRuedaA]

WIP