Added

• Optional RelationNature enum (FRIENDLY, NEUTRAL, HOSTILE) to the model package. Each TeamRelation constant carries a built-in default nature which may be queried with getDefaultNature().
• Consumer override support: TeamRelation#setNatureOverride(RelationNature) and TeamRelation#getNature() - allows server or provider code to re-categorise a relation at runtime. Passing null to setNatureOverride clears the override and restores the builtin default. Overrides are visible JVM-wide because enum constants are singletons.
• Unit tests: TeamRelationTest covering default natures and override behaviour.

Changed

• TeamsAPI.API_VERSION bumped to 2.1.0.

Migration
No behavioural changes to existing TeamRelation helpers: isFriendly() and isHostile() remain unchanged and existing consumers require no changes. Providers that wish to reclassify relations (for example treating TRUCE as NEUTRAL) may call setNatureOverride(...) during initialisation.