[FEATURE] Add option to disable /resume tab completion suggestions

Summary

When typing /resume and pressing Tab, Claude Code shows a list of previous session titles as autocomplete candidates. There should be an option to disable this behavior.

Current Behavior

1. Type /resume in the input
2. Press Tab
3. A list of previous session titles appears as completion suggestions (e.g., nextjs-16.2-upgrade-analysis)

Expected Behavior

An option to suppress the /resume tab completion candidates, so pressing Tab after /resume does nothing (or the user can simply press Enter to get the interactive session picker).

Use Case

• The autocomplete candidates are distracting and not useful when you already know you want the interactive picker
• Old session titles clutter the completion list
• promptSuggestionEnabled: false in settings.json only disables prompt ghost text suggestions — it has no effect on slash command argument completion

Proposed Solution

Add a setting to disable slash command tab completion, or at minimum allow disabling it for /resume specifically. For example:

{
  "slashCommandCompletionEnabled": false
}

Environment

• Claude Code: 2.1.100
• macOS (Darwin 25.4.0)
• Terminal: CLI