Chrome Integration: Clearer Offer Flow

The Claude-in-Chrome integration now has cleaner offer and rejection messaging:

• The startup offer now shows "Yes, use my browser" and "No, keep browser tools off" options explicitly
• "Turn browser tools off for future sessions" guidance added
• "This session is in Auto mode, so an AI classifier approves routine browser actions — you are only prompted when it is unsure" message
• "This session is in Don't Ask mode, so browser actions that need approval are skipped rather than prompted" message
• "Site-level permissions come from the Chrome extension" clarification
• The old hardcoded system-prompt paragraph about the claude-in-chrome skill has been removed; Chrome integration is now handled through the normal MCP machinery