refactor(domain): rename stadium_name/stadium_capacity to arena_name/arena_capacity

[NicoRuedaA]

Problem or opportunity

Team struct in domain/src/team.rs uses stadium_name: String and stadium_capacity: u32. League of Legends teams compete in arenas, not stadiums.

Proposed solution

1. Add �rena_name: String and �rena_capacity: u32 to Team.
2. Add #[serde(alias = "stadium_name")] and #[serde(alias = "stadium_capacity")].
3. SQL migration (v033) adds new columns and copies data from old columns.
4. Keep old columns during transition; remove in future migration.

UX impact

• Team profile screen shows "Arena" instead of "Stadium".
• World editor fields updated.

Acceptance criteria

• �rena_name and �rena_capacity added to Rust type with aliases
• v033 SQL migration created
• Frontend uses new field names
• Old stadium columns remain in DB for one release cycle

Scope

Data / provenance