feat(plugins): add Velocity proxy and Fabric/Forge/NeoForge/Paper integration mods

Server-side integration plugins: the Velocity proxy plugin plus Fabric, Forge, NeoForge, and Paper mods with a shared module. Gradle build output is not tracked.

plugins/neoforge/build.gradle

@@ -0,0 +1,41 @@
+plugins {
+    id 'net.neoforged.gradle.userdev' version '7.1.38'
+    id 'java'
+}
+
+group = 'best.lolicon.felis'
+version = '0.1.0'
+
+// NeoForge 20.4 (MC 1.20.4) is a Java-17 line. The Gradle daemon runs on JDK 17,
+// so toolchain 17 resolves to the running JVM with no auto-provisioning.
+java {
+    toolchain.languageVersion = JavaLanguageVersion.of(17)
+}
+
+repositories {
+    mavenCentral()
+    maven {
+        name = 'NeoForged'
+        url = 'https://maven.neoforged.net/releases'
+    }
+}
+
+dependencies {
+    // NeoForge bundles MC at Mojang mappings — same MC class/method names as the
+    // Fabric and Forge modules, so the command handler below is uniform with them.
+    implementation 'net.neoforged:neoforge:20.4.251'
+}
+
+// The zero-dependency link core is compiled in. NeoForge runs Mojang mappings at
+// runtime, so there is no reobf step — the jar straight out of `build` is the deliverable.
+sourceSets {
+    main {
+        java {
+            srcDir '../shared/src/main/java'
+        }
+    }
+}
+
+tasks.withType(JavaCompile).configureEach {
+    options.encoding = 'UTF-8'
+}