Modernize zKoth for supported Paper 26.2 APIs

[GerwinVerkerk]

Objective

Move zKoth from removed, internal, and deprecated Bukkit/Bungee/NMS paths to supported Paper 26.2 APIs while preserving existing gameplay behavior.

Scope

• replace reflective NMS action-bar, item/NBT, and version-routing code with supported Paper APIs;
• use Adventure components for legacy-formatted chat, titles, action bars, inventory titles, item names, and lore;
• migrate profiles, materials, enchants, potion effects, inventory holders, plugin lifecycle calls, and related hook calls to current APIs;
• keep a read-only legacy item decoder for existing saved rewards while writing new items with Paper's byte serializer;
• update compilation to exact Paper 26.2 build 112 and fail on deprecated/removal/unchecked Java API use;
• add regression coverage for legacy and hex color conversion.

Keeping the old reflection/version matrix and adding another 26.2 branch was considered, but rejected: those internals are not a supported Paper contract and would continue to break across server updates.

Verification

• ./gradlew --no-daemon clean build — passed on Java 25
• 2 JUnit tests passed, 0 failures/skips
• compilation passed with deprecation, removal, and unchecked warnings treated as errors
• source scan found no remaining NMS/CraftBukkit/Bungee chat imports or removed version helper usage
• git diff --check — passed

Compatibility and operational notes

• Target runtime: Paper 26.2 / Java 25.
• No command, permission, schema, or economy changes.
• Existing legacy serialized item rewards remain readable.
• Newly saved item strings use a paper: format and are not readable by older zKoth builds; operators should back up configuration before downgrading.
• Optional hook dependencies and load order remain unchanged.
• GUI, inventory, movement/capture, client rendering, and reward delivery still require real-player acceptance after deployment.

Rollback

Revert the commit and restore configuration saved before first use of the new item serializer. A JAR-only downgrade is safe only if no rewards were re-saved in the new paper: format.