Allow hiding/removing built-in MCP integrations from /mcp dialog

Problem

The /mcp dialog shows built-in integrations (claude.ai, Gmail, Google Calendar) that cannot be removed or hidden, even when claudeInChrome is set to false in settings.

• claude mcp remove doesn't work on them ("No MCP server found")
• claude mcp list doesn't show them (they're not user-configured)
• Setting "claudeInChrome": false disables the functionality but doesn't hide the entries

Expected behavior

If a user has opted out of Chrome integrations via "claudeInChrome": false, these entries should not appear in the /mcp dialog at all. Ideally, users should be able to fully remove any integration they don't want to see.

Current behavior

Three non-removable entries permanently visible in /mcp:

• claude.ai
• Gmail · △ needs authentication
• Google Calendar · △ needs authentication

Environment

• Claude Code CLI
• macOS (Darwin 25.3.0)