MEMORY: /memory slash command (edit each scope in $EDITOR)

[Hmbown]

Part of #489.

Summary

Add a /memory slash command that lets the user open any memory file in $EDITOR (or $VISUAL) without leaving the TUI.

Subcommands

• /memory — interactive picker (user / project / local)
• /memory user — edit ~/.deepseek/AGENTS.md
• /memory project — edit <repo>/AGENTS.md (creating it if missing)
• /memory local — edit <repo>/AGENTS.local.md (creating + adding to .gitignore if missing)
• /memory list — show what's currently loaded with sizes

Reference

reference-cc/src/commands/memory/memory.tsx:14-89.

Acceptance

• Editor spawn works on macOS/Linux/Windows.
• Parent dirs are auto-created.
• Re-loads memory after the editor exits — no client restart needed.

Effort: S (~150 LoC).

[Hmbown]

Shipped on fix/v0.8.8-hotfixes (7547d16). Leaving open until maintainer smoke-tests v0.8.8 — close on verification.

[Hmbown]

Fixed in 7547d16 on fix/v0.8.8-hotfixes.