[Bug] /effort command applies globally instead of per-session

Bug Description
/effort sets the effort level for all sessions, not just the current one.

Environment Info

• Platform: linux
• Terminal: ghostty
• Version: 2.1.118
• Feedback ID: 5d5f6112-8b52-4f5f-b394-1d6a2901082d

Errors

[{"error":"Error: NON-FATAL: Lock acquisition failed for /home/sjunot/.local/share/claude/versions/2.1.118 (expected in multi-process scenarios)\n    at ii$ (/$bunfs/root/src/entrypoints/cli.js:2758:2177)\n    at R46 (/$bunfs/root/src/entrypoints/cli.js:2758:1257)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-04-23T21:02:09.785Z"}]