Desktop app `/` slash commands lack parity with TUI

Problem

Typing / in the Mac desktop app composer shows a smaller set of slash commands than the TUI, with no way to reach the missing ones.

Current behavior (v2.0.8, verified in source)

Desktop / suggestions come from packages/app/src/composer/model.ts (slashCommands memo): custom commands from command.list plus only app builtins registered with a slash: property:

• use-session-commands.tsx: /new, /undo, /redo, /compact, /fork, /export, /open, /terminal, /mcp
• composer/commands.tsx: /model, /agent

Missing TUI builtins (per https://opencode.ai/docs/tui#commands): /init, /share, /unshare, /sessions, /models (desktop has singular /model picker instead), /themes, /thinking, /details, /editor, /connect, /help, /exit, plus the new /btw.

Custom commands (opencode.json command section / commands/ markdown) only send prompt templates to the server, so client-action commands like /share, /sessions, /themes cannot be recreated by users.

Expected

/ in the desktop composer should offer the same built-in commands as the TUI (mapping to the desktop equivalent where the UI differs, e.g. /models -> model picker, /themes -> theme picker), or document which are intentionally desktop-excluded.

Version

Desktop 2.0.8 (arm64, Mac), server/CLI 2.0.8

Start in packages/app/src/composer/model.ts, especially the slashCommands memo, then inspect use-session-commands.tsx and composer/commands.tsx alongside the TUI command list in the issue. Done means the desktop composer exposes equivalent built-in commands with desktop mappings, or clearly documents which commands are intentionally excluded.