fix: remove everything that requires a privileged intent

[wescopeland]

Fixes #58.

[greptile-apps]

Greptile Summary

Removes privileged Discord intents and dependent legacy features.

• Removes prefix commands and member-enumeration features.
• Migrates mem and rules to slash commands.
• Retains metadata-only auto-publishing.

Confidence Score: 5/5

The PR appears safe to merge.

Removed infrastructure has no remaining callers; replacement commands satisfy existing loading and deployment contracts.

_{Reviews (1): Last reviewed commit: "fix: remove everything that requires a p..." | Re-trigger Greptile}