Add project sources and fix .gitignore for Gradle build

- .gitignore: exclude build/, .gradle/, IDE files, OS files
- Gradle 8.12 multi-version build system (Fabric Loom 1.9.1)
- Full source: JustASplash entrypoint, config, asset cache, keybind, renderer, sound, image loaders (PNG/WebP), WindowMixin
- Resources: fabric.mod.json, mixins, localization (en/ru), default splash.png + sounds, icon
- Refactored from me.sashegdev to net.anomaly.justasplash package

.gitignore

@@ -1,45 +1,38 @@
-# ---> Java
-# Compiled class file
-*.class
-
-# Log file
-*.log
-
-# BlueJ files
-*.ctxt
-
-# Mobile Tools for Java (J2ME)
-.mtj.tmp/
-
-# Package Files #
+# Gradle
+build/
+.gradle/
 *.jar
 *.war
 *.nar
 *.ear
-*.zip
-*.tar.gz
-*.rar
 
-# virtual machine crash logs, see http://www.java.com/en/download/help/error_hotspot.xml
+# IDE
+.idea/
+*.iml
+*.ipr
+*.iws
+.vscode/
+.settings/
+.project
+.classpath
+bin/
+
+# OS
+.DS_Store
+Thumbs.db
+*.swp
+*.swo
+*~
+
+# Env
+.env
+.env.local
+
+# Logs
+*.log
 hs_err_pid*
 replay_pid*
 
-# ---> Maven
-target/
-pom.xml.tag
-pom.xml.releaseBackup
-pom.xml.versionsBackup
-pom.xml.next
-release.properties
-dependency-reduced-pom.xml
-buildNumber.properties
-.mvn/timing.properties
-# https://github.com/takari/maven-wrapper#usage-without-binary-jar
-.mvn/wrapper/maven-wrapper.jar
-
-# Eclipse m2e generated files
-# Eclipse Core
-.project
-# JDT-specific (Eclipse Java Development Tools)
-.classpath
-
+# Misc
+*.ctxt
+.mtj.tmp/