fix: add missing pom.xml to Java Maven test fixture

[mashraf-222]

Summary

The Java Maven test fixture in tests/test_languages/fixtures/java_maven/ was missing a pom.xml file, causing Maven build tool detection to fail.

Problem

The test_detect_fixture_project test was failing because:

• Build tool detection checks for pom.xml to identify Maven projects
• The fixture directory had no pom.xml, so detection returned BuildTool.UNKNOWN instead of BuildTool.MAVEN
• Test expected BuildTool.MAVEN but got BuildTool.UNKNOWN

Solution

Added a standard Maven pom.xml with:

• JUnit 5 dependencies (junit-jupiter-api, junit-jupiter-engine v5.9.3)
• Maven Surefire plugin (v2.22.2) for test execution
• Java 11 compiler configuration
• UTF-8 encoding
• Project metadata (groupId: com.example, artifactId: calculator)

Impact

• ✅ Fixes test_detect_fixture_project test
• ✅ All 323 Java tests now pass (7 skipped)
• ✅ Enables proper Maven project detection in test suite
• ✅ No changes to production code, test-only fix

[mashraf-222]

Closing PR - Changes Already Merged

This PR is no longer needed because the changes have already been incorporated into omni-java through other PRs.

What Happened:

1. Original Goal: Add missing pom.xml to tests/test_languages/fixtures/java_maven/
2. Current State: The file was already added to omni-java (likely through PR feat: add import-based test discovery for Java #1268 or a related fix)
3. After Merge Conflict Resolution: This branch now has 0 diffs compared to omni-java

Verification:

$ git diff origin/omni-java..HEAD
# No output - zero differences

Conclusion:

✅ The bug is fixed - pom.xml exists in omni-java
✅ All tests pass (336 passed, 7 skipped)
✅ This PR is now redundant

Closing as the work is already complete through other merged PRs. Thank you for the review and approval!