chore: remove .agent-mail-project-id and add to gitignore

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: blackbxdev

.agent-mail-project-id

@@ -64,6 +64,7 @@ AGENTS.md
 
 # Agent workspaces (agent-mail coordination)
 .agents/
+.agent-mail-project-id
 
 # Task drafts and PRDs
 tasks/