security: remove .mcp.json from git tracking and add to .gitignore

.mcp.json contains MCP server credentials (API tokens, passwords) that
should never be version-controlled. File remains on disk for runtime use.

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

Author: Oliver Miranda

.gitignore

@@ -21,6 +21,7 @@ groups/global/*
 # Secrets
 *.keys.json
 .env
+.mcp.json
 
 # Temp files
 .tmp-*