Feature: Allow disabling global ~/.claude/CLAUDE.md per session

Problem

~/.claude/CLAUDE.md is always loaded automatically for every session. There is no way to opt out of loading global instructions for a specific session.

Use Case

Users may have comprehensive global instructions in ~/.claude/CLAUDE.md that are useful for most workflows, but sometimes need a "clean" session without those instructions — for example:

• Debugging whether global instructions are causing unexpected behavior
• Working on tasks where global instructions are irrelevant or conflicting
• Starting a minimal session for quick one-off tasks

Proposed Solution

Add a CLI flag to skip loading the global CLAUDE.md file, e.g.:

claude --no-global-instructions
# or
claude --skip-global-memory

Alternatively, an environment variable could work:

CLAUDE_NO_GLOBAL_INSTRUCTIONS=1 claude

Current Workaround

The only option today is to manually rename/move the file before starting a session and restore it afterward:

mv ~/.claude/CLAUDE.md ~/.claude/CLAUDE.md.bak
claude
mv ~/.claude/CLAUDE.md.bak ~/.claude/CLAUDE.md

This is error-prone and inconvenient.