Resolve @self in queue commands to avoid simple_expansion prompts

[blipinsk]

Summary

• Add @self keyword that codemob queue resolves internally to the current mob name via CurrentMobName()
• Update /remove and /drop slash commands to use codemob queue remove @self instead of codemob queue remove "$CODEMOB_MOB"
• Eliminates Claude's simple_expansion permission prompt since the command is now a plain literal string with no variable expansion

Closes #29

Test plan

• Run /drop from inside a mob - should queue remove without permission prompt
• Run /remove and select the current mob - same behavior
• Run codemob queue remove @self manually from inside a mob - resolves correctly
• Run codemob queue remove @self outside a mob - errors with "@self: not inside a mob"
• Run codemob init and verify regenerated slash commands use @self

[blipinsk]

Q: does codemob info clear queue 🤔