feat(base): adopt Purpur distribution naming

BREAKING CHANGE: New release assets use purpur-base-<version>.jar. Runtime SpigotBase identity, data folders, permissions and persistent item keys remain unchanged. Replace the old JAR rather than loading both distributions.

src/test/java/games/dmg/spigotbase/PurpurDistributionTest.java

@@ -0,0 +1,49 @@
+package games.dmg.spigotbase;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import java.io.DataInputStream;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Map;
+import java.util.jar.JarFile;
+import org.junit.jupiter.api.Test;
+import org.yaml.snakeyaml.Yaml;
+
+/** Distribution branding is deliberately independent of persistent/runtime plugin identity. */
+class PurpurDistributionTest {
+    @Test
+    void packagesJava25UnderNewNameWithoutChangingRuntimeIdentityOrBundlingTheApi() throws Exception {
+        Path artifact = Path.of(System.getProperty("distribution.jar"));
+        String version = System.getProperty("distribution.version");
+        assertEquals("purpur-base-" + version + ".jar", artifact.getFileName().toString());
+        try (var jar = new JarFile(artifact.toFile())) {
+            Map<?, ?> metadata = new Yaml().load(jar.getInputStream(jar.getJarEntry("plugin.yml")));
+            assertEquals(version, metadata.get("version"));
+            assertEquals("SpigotBase", metadata.get("name"), "Do not orphan the existing plugin data folder or default namespace");
+            assertEquals("games.dmg.spigotbase.SpigotBasePlugin", metadata.get("main"));
+            assertTrue(((Map<?, ?>) metadata.get("permissions")).containsKey("spigotbase.admin"));
+            try (var bytecode = new DataInputStream(jar.getInputStream(
+                jar.getJarEntry("games/dmg/spigotbase/SpigotBasePlugin.class")))) {
+                assertEquals(0xCAFEBABE, bytecode.readInt());
+                bytecode.readUnsignedShort();
+                assertEquals(69, bytecode.readUnsignedShort(), "Plugin bytecode must target Java 25");
+            }
+            assertFalse(jar.stream().anyMatch(entry -> entry.getName().startsWith("org/bukkit/")
+                || entry.getName().startsWith("org/purpurmc/") || entry.getName().endsWith("Test.class")));
+        }
+    }
+
+    @Test
+    void releaseAndCiAgreeWithThePurpurDistributionNameAndToolchain() throws Exception {
+        String build = Files.readString(Path.of("build.gradle.kts"));
+        assertTrue(build.contains("purpur-api:26.2.build.2618-stable"));
+        assertFalse(build.contains("org.spigotmc:spigot-api"));
+        for (String workflow : new String[] {"ci.yml", "release.yml"}) {
+            String content = Files.readString(Path.of(".gitea/workflows", workflow));
+            assertTrue(content.contains("java-version: 25"));
+            assertTrue(content.contains("purpur-base-"), workflow + " must publish the renamed distribution");
+            assertFalse(content.contains("spigot-base-"), workflow + " must not look for the old JAR filename");
+        }
+    }
+}