Needlessly redundant command palette and slash command definitions

[kitlangton]

Command palette entries and slash command autocomplete are duplicated:

• Command registrations: app.tsx, routes/session/index.tsx, component/prompt/index.tsx
• Slash commands: component/prompt/autocomplete.tsx (~130 lines hardcoded)

Visibility logic is duplicated across both (e.g., share/unshare conditions).