chore: add ECC plugin dirs to .gitignore

Keep Claude Code agent/command/hook/rule/skill configs local-only.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -39,4 +39,13 @@ report.xml
 *.key
 
 # Internal plan (not for repo)
-.claude/plan.md
+.claude/plan.md
+
+# ECC plugin (local only)
+.claude/agents/
+.claude/commands/
+.claude/examples/
+.claude/hooks/
+.claude/mcp-configs/
+.claude/rules/
+.claude/skills/