Add initial backend, CLI, and frontend scaffold

Bootstrap repository with multi-component scaffolding: a Spring Boot backend (Maven wrapper, pom.xml, BackendApplication, test, resources, .gitignore/.gitattributes), a Go CLI app using Cobra (root + subcommands: diff, log, login, pull, push, set, unset), prebuilt CLI binaries and a build script, and a Next.js frontend (configs, package.json, styles, pages, and static assets). This commit provides the skeleton for development across backend, CLI, and frontend components.

backend/src/main/java/com/envsync/backend/BackendApplication.java

@@ -0,0 +1,13 @@
+package com.envsync.backend;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class BackendApplication {
+
+	public static void main(String[] args) {
+		SpringApplication.run(BackendApplication.class, args);
+	}
+
+}

backend/src/main/resources/application.properties

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+spring.application.name=backend

backend/src/test/java/com/envsync/backend/BackendApplicationTests.java

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+package com.envsync.backend;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.boot.test.context.SpringBootTest;
+
+@SpringBootTest
+class BackendApplicationTests {
+
+	@Test
+	void contextLoads() {
+	}
+
+}