feat: Add AGENTS.md

Author: iseppala

AGENTS.md

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+# 30 Seconds of Java - Priming Context for AI Agents
+
+## Quick Overview
+30 Seconds of Java is a curated collection of reusable, copy-pasteable Java 21 snippets designed to be understood in 30 seconds or less. These snippets cover a wide range of common tasks and are automatically published to the project's website via the `README.md` file.
+
+## Stack
+- **Language**: Java 21
+- **Build System**: Gradle 8.x
+- **Testing**: JUnit 5 (Jupiter), Hamcrest
+- **Quality Assurance**: Checkstyle, SonarCloud
+
+## Trusted Sources
+- [Java 21 SE API Documentation](https://docs.oracle.com/en/java/javase/21/docs/api/index.html)
+- [JUnit 5 User Guide](https://junit.org/junit5/docs/current/user-guide/)
+- [Gradle User Manual](https://docs.gradle.org/current/userguide/userguide.html)
+- [Hamcrest Matchers Reference](http://hamcrest.org/JavaHamcrest/javadoc/2.2/org/hamcrest/Matchers.html)
+
+## Structure
+- `/src/main/java/{category}/`: Source code for the snippets, organized by category (e.g., `string`, `math`, `network`).
+- `/src/test/java/{category}/`: Unit tests for each snippet.
+- `README.md`: The main documentation file containing all snippets, used for website generation.
+- `build.gradle`: Project dependencies and build configuration.
+
+## Patterns
+- **Stateless Utility Methods**: Implement snippets as `public static` methods within a dedicated class.
+- **Locale Independence**: Always use `Locale.ENGLISH` when formatting strings (e.g., `String.format`) to ensure consistent behavior across different environments.
+- **Modern Java Features**: Leverage Java 21 features (e.g., `var`, `Stream` API, modern `HttpClient`) where appropriate.
+- **Focused Scope**: Each snippet class should perform exactly one task or a small set of highly related tasks.
+
+## Anti-patterns
+- **External Dependencies**: Do not add third-party libraries; rely exclusively on the Java Standard Library.
+- **Global State**: Snippets must not maintain or depend on mutable global state.
+- **Interactive Logic**: Avoid snippets that require terminal input or user interaction.
+- **Untested Code**: Every snippet must be accompanied by a comprehensive JUnit test.
+
+## Example Snippet
+A complete snippet implementation consists of three parts:
+
+1. **Source Code** (`src/main/java/string/FormatBytesSnippet.java`):
+```java
+public class FormatBytesSnippet {
+  public static String formatBytes(long bytes) {
+    double kb = 1024;
+    // ... logic ...
+    return String.format(Locale.ENGLISH, "%.2f MB", bytes / mb);
+  }
+}
+```
+
+2. **Test File** (`src/test/java/string/FormatBytesSnippetTest.java`):
+```java
+class FormatBytesSnippetTest {
+  @Test
+  void formatBytes() {
+    assertEquals("1.46 MB", FormatBytesSnippet.formatBytes(1536000));
+  }
+}
+```
+
+3. **README.md Entry**:
+```markdown
+### Format Bytes
+
+```java
+// [Full code of the snippet]
+```
+```