docs: link CLAUDE.md to AGENTS.md

Claude Code reads CLAUDE.md, so it did not pick up the shared agent
instructions in AGENTS.md. Check in CLAUDE.md as a symlink to AGENTS.md
and drop its .gitignore entry.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: manuzhang

.gitignore

@@ -38,7 +38,6 @@ cmake-build-release/
 
 # AI
 AGENTS.md
-CLAUDE.md
 GEMINI.md
 .claude/
 .cursor/

CLAUDE.md

@@ -0,0 +1 @@
+AGENTS.md