feat: add AI-based security suggestion engine and CLI integration

Introduce new package org.egothor.methodatlas.ai providing AI-assisted
classification of JUnit tests for security relevance.

Key changes:
- add AI suggestion engine, provider abstraction, and provider clients
  (OpenAI-compatible, Ollama, Anthropic)
- implement strict JSON prompt/response contract and taxonomy handling
- integrate AI enrichment into MethodAtlas CLI output (CSV and plain
  modes)
- add configuration via AiOptions and CLI flags
- add comprehensive JUnit + Mockito test coverage for AI components
  and CLI integration scenarios
- add realistic test fixtures for security-related test classes
- update Gradle configuration for Mockito agent support on JDK 21+
- provide complete Javadoc for the AI module

The AI layer is optional and degrades gracefully when providers
are unavailable or responses fail.

src/test/resources/fixtures/PathTraversalValidationTest.java.txt

@@ -0,0 +1,63 @@
+package com.acme.storage;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.nio.file.Path;
+
+import org.junit.jupiter.api.Tag;
+import org.junit.jupiter.api.Test;
+
+public class PathTraversalValidationTest {
+
+    @Test
+    @Tag("security")
+    @Tag("validation")
+    void shouldRejectRelativePathTraversalSequence() {
+        String userInput = "../secrets.txt";
+
+        IllegalArgumentException ex = assertThrows(IllegalArgumentException.class, () -> {
+            if (userInput.contains("..")) {
+                throw new IllegalArgumentException("Path traversal attempt detected");
+            }
+        });
+
+        assertEquals("Path traversal attempt detected", ex.getMessage());
+    }
+
+    @Test
+    @Tag("security")
+    @Tag("validation")
+    void shouldRejectNestedTraversalAfterNormalization() {
+        String userInput = "reports/../../admin/keys.txt";
+        Path normalized = Path.of("/srv/app/uploads").resolve(userInput).normalize();
+
+        IllegalArgumentException ex = assertThrows(IllegalArgumentException.class, () -> {
+            if (!normalized.startsWith(Path.of("/srv/app/uploads"))) {
+                throw new IllegalArgumentException("Escaped upload root");
+            }
+        });
+
+        assertEquals("Escaped upload root", ex.getMessage());
+    }
+
+    @Test
+    @Tag("security")
+    @Tag("validation")
+    void shouldAllowSafePathInsideUploadRoot() {
+        String userInput = "reports/2026/statement.pdf";
+        Path normalized = Path.of("/srv/app/uploads").resolve(userInput).normalize();
+
+        boolean allowed = normalized.startsWith(Path.of("/srv/app/uploads"));
+
+        assertEquals(true, allowed);
+    }
+
+    @Test
+    void shouldBuildDownloadFileName() {
+        String accountId = "ACC-42";
+        String fileName = accountId + "-statement.pdf";
+
+        assertEquals("ACC-42-statement.pdf", fileName);
+    }
+}