Migrate ServerFeatures to Adventure 5

[remdui]

Summary

Migrates ServerFeatures from Adventure 4.26.1 to Adventure 5.2.0 and moves the platform target from Paper 26.1.2 to Paper 26.2, the first Paper release line that natively ships Adventure 5.

Changes

• import net.kyori:adventure-bom:5.2.0
• align Adventure API, MiniMessage, Gson, legacy and plain serializers through the BOM
• target paper-api:26.2.build.65-beta
• update NBTComponent inspection for the Adventure 5 generic signature
• exclude EssentialsX's legacy Adventure platform bridge and obsolete serializer transitives
• enforce that no Adventure 4.x core modules resolve transitively
• add an explicit CI dependency-tree check and persistent Maven diagnostics

Root cause

Paper 26.1.2 is compiled for Adventure 4. Forcing Adventure 5 into that dependency graph removes MessageType while inherited Paper API signatures still reference it, which caused widespread proxy-based test failures. Paper 26.2 natively ships Adventure 5 and removes that binary mismatch.

Compatibility impact

This changes the minimum supported Paper line to 26.2. Adventure remains provided and is supplied by Paper at runtime.

Validation

• mvn -U -B -ntp verify
• 391 tests passed, 5 skipped
• CI lint passed
• resolved Adventure dependency graph contains only Adventure 5.2.0 core modules