ORC-2125: Add .claude to .gitignore

### What changes were proposed in this pull request?

This PR adds `.claude/` to `.gitignore`.

### Why are the changes needed?

`Anthropic` has a promotion for open source projects. I hope we can help the developers. [Claude Code](https://claude.ai/claude-code) creates a `.claude/` directory for project-level configuration and context. This directory should not be tracked in version control.

- https://claude.com/contact-sales/claude-for-oss

> Open-source maintainers and contributors keep the ecosystem running. The Claude for Open Source Program is our way of saying thank you for all your hard work, with 6 months of free Claude Max 20x.
> - Maintainers: You’re a primary maintainer or core team member of a public repo with 5,000+ GitHub stars or 1M+ monthly NPM downloads. You've made‍ commits, releases, or PR reviews within the last 3 months.

### How was this patch tested?

Manual verification that `.claude/` directory is ignored by git.

### Was this patch authored or co-authored using generative AI tooling?

Generated-by: Claude Code (Claude Opus 4.6)

Closes #2576 from dongjoon-hyun/ORC-2125.

Authored-by: Dongjoon Hyun <dongjoon@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

Author: dongjoon-hyun

.gitignore

@@ -11,6 +11,7 @@ dependency-reduced-pom.xml
 .idea
 .vscode
 .DS_Store
+.claude/
 .java-version
 java/bench/data
 *.swp