feat(tree-feller): migrate distribution and local harness to Purpur

BREAKING CHANGE: New releases require Java 25/Purpur 26.2 and use purpur-tree-feller-<version>.jar. Runtime TreeFeller identity, data folder, progression and felling/undo behavior are unchanged. Replace the old JAR rather than installing both distributions. The local harness now selects Purpur 2618; its stored worlds and operator/port/RCON settings are preserved. No containers are started by this migration.

.gitea/workflows/ci.yml

@@ -17,7 +17,7 @@ jobs:
         uses: actions/setup-java@v4
         with:
           distribution: temurin
-          java-version: 17
+          java-version: 25
           cache: gradle
 
       - name: Validate conventional commits
@@ -35,6 +35,6 @@ jobs:
       - name: Upload development artifact
         uses: actions/upload-artifact@v3
         with:
-          name: tree-feller-${{ github.sha }}
+          name: purpur-tree-feller-${{ github.sha }}
           path: build/libs/*.jar
           if-no-files-found: error