chore: add shared agent config layout

[yiliu30]

Summary

• add repository agent guidance files and keep only CLAUDE.md
• share skills across Claude, Codex, and OpenCode via symlinks
• ignore local Claude config and local planning notes

Verification

• checked staged diffs before each commit
• verified .codex/skills and .opencode/skills resolve to .claude/skills
• no code/test changes; no test suite run

[Copilot]

Pull request overview

Adds a shared, repo-level agent guidance entrypoint and ignores local agent/planning artifacts to standardize how different coding agents operate in this repository.

Changes:

• Add AGENTS.md with repository build/test/style guidance for agents.
• Add CLAUDE.md as a minimal entrypoint referencing AGENTS.md.
• Update .gitignore to ignore local Claude config (CLAUDE.local.md) and local planning notes (docs/plan/).

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 2 comments.

File	Description
CLAUDE.md	New entrypoint that references shared agent guidance (@AGENTS.md).
AGENTS.md	New consolidated instructions for agents (project, install, testing, style, conventions).
.gitignore	Ignores local Claude config and local planning directory.

[wenhuach21]

please review

[yiliu30]

/azp run Unit-Test-CUDA-AutoRound

[azure-pipelines]

Azure Pipelines could not run because the pipeline triggers exclude this branch/path.